It's easy: würden = would / hätten = would have.

• Das würde ich nicht sagen = I wouldn't say that.
• Er würde es kaufen = He would buy it.
• Wir hätten mehr Geld = we would have more money.
• Ich hätte das nicht gemacht = I wouldn't have done that.

Modal verbs has its own form (haben>hätten (would have), sein>wäre (would be), mögen>möchte (would like), können>könnten (could)). For other verbs you combine würden + verb = would + verb (würden sagen, würden kaufen...).

• "hätte/wäre" is used for the past / conditional II: "Ich hätte viel Geld gewonnen, wenn ich auf ihren Sieg gewettet hätte." ("I would have won a lot of money, if I had placed a bet on their victory."), "Ich wäre joggen gegangen, wenn es heute Morgen nicht so kalt gewesen wäre." ("I would have gone running, if it hadn't been so cold this morning.") Whether you use "hätte" or "wäre" depends on the perfect form the verb takes, e.g. "ich habe gewonnen/gewettet", "ich bin gegangen, es ist gewesen"

• "würde" is used for the present/future / conditional I: "Ich würde dir Geld geben, wenn du es nicht immer für Wetten ausgeben würdest." ("I would give you money, if you didn't always spend it on bets."), "Ich würde mit dir ins Kino gehen, wenn du hübscher wärst." ("I would go to the cinema with you, if you were prettier.")

Note that "hätte" can be a form of conditional I as well, if it's a full / non-auxiliary verb: "Ich würde dir Geld geben, wenn ich welches hätte." ("I would give you money, if I had any.")

Thank you TaylorHenrique and Stepintime, it's completely clear for me now and actually quite simple (not in execution though :) )

I'm not taking German right now, but dude, I love your IMVU avatar! Lol.