Ok, let me give it a try.Squares show an influential energy between two planets that's like "wild honey to a bear" - while the bees are representative for the blockage (source of tension). Let's say he's a cartoon bear (personification), cause eventually the bear will have to learn to live with the bees in harmony, so it's not enough for him to become a Beekeeper - the bees have to feel natural to him in a complementary way. By its nature - the energy of Square can be closest to the energy of a Trine (gone wrong).
Now imagine two teenagers who were recently accepted to a good college, one it's called Trine the other Square. Both of them have similar potential, but Trine is part of a rich family who spoils him with their support and same goes for his friends, while Square - has none of that, except the desire to finish that college - but he's gonna have to work hard to get there, a troublesome path - to say at least. Yet, once he gets there - especially since he worked so hard and the things he had to put up with, he's gonna feel a real sense of pride. There was this movie with Will Smith called "The Pursuit of Happyness" - which is kinda representative for a Square, and the ending for what it means to get there: http://www.youtube.com/watch?v=56fngopihOo And that's why Squares are supposedly better than Trines if you manage to overcome them.
Oppositions are quite different by nature - the term opposite is self-explanatory for what they stand for, as in their both opposite forces. So in their case - it's not a matter of
being complimentary to each-other but "accepting the differences in each-other". Cause it's not just about the planets involved but also the houses and signs in which they fall. And since a Opposition is measured at 180 degrees both the Sign and the House falls in opposition, but this oppositions are already predefined by the zodiac both in terms of Houses and Signs. Though, it's also worth mentioning that - some oppositions are easier to handle than others, showing more room for positive results - for example:
House 3 Gemini opposing House 9 Sagittarius (Nice!)
...compared to:
House 1 Aries opposing House 7 Libra (Ouch!)
Let me put it in a different way. Let's say we he have an architect called Saturn and a painter called Venus. They both have a hobby in common - "a passion for cooking" and they're both part part of a cooking class. They felt connected - and decided to form a team, but - each in their own way kept making mistakes that ruined the food - or didn't make it quite right (neither of them was pleased with the results). It just felt right, the guts tell them - they could do it but every fail made them doubt their efforts, making them feel as they're lousy cooks. So, they kept trying and with every step they felt like they're getting closer (the food being better and better) - while every fail felt just as bad, dabbling with feelings of hate for themselves and the work they were doing - instead of love. Basically, that's a Square - it can bring a lot of frustration, but once you overcome it - the outcome might prove to be even better than a Trine - the results, their cooking being close to perfection (as one would put it - to die for).
Same story, but if we're to talk about opposition - even though they feel attraction for each-other, they work separately - each doing their own thing - which can be completely different than what the other is doing. Let's say - Saturn is a meat lover and Venus a vegetarian - both really fond of their chosen lifestyle, so a change in the opposite direction - would be out of the question. Now this, can imply some tension - where one could make the other feel bad for the choice he made. So, if they're to overcome their differences (the opposition) they just have to accept each-other for whom they are.
Squares are more active, they keep popping up - which makes them a lot harder to deal with compared to oppositions - which are more passive and rise on the surface on certain occasions (they don't feel like an active issue).
In a way - you could take a Square like a Trine gone bad - it has the same potential (more showy if you overcome it), but you have to restore the order - as "it's a mess" out of the box. That being said, the trine between Venus and Saturn - is more relational nature (it's same with square) - where one is in control of his feelings, but also good at appraising the person in front of him and how to deal with it (a real life James Bond). While with square - the feelings can be overwhelming, it can imply a certain level of shyness (the Venus influence) in dealing with those he finds attractive, a defensive shyness - resulted from a anxiety (Saturn influence) of the moment and a fear of rejection resulted from lack of self-love. As for Opposition - still emotional of nature but - has more to do with lack of self-worth. The harshness of Saturn feels to rough on the delicate nature of Venus and viceversa. So, in terms of opposition you have to accept both the delicate nature of Venus and the harshness of Saturn - as separate parts of yourself, appreciate them individually for what they're worth and that can help you grow. It can help you appraise - both yourself and the people around you better - which gives you more control over your emotions in relation with others, as that can be a problem in early stages of life. Either by being attracted to authority figures - for that fact alone, or by being to harsh on those who show appreciation for you... which can imply a dysfunctional behaviour.
I hope this helps in clearing some things.