I invest $100 for 20% of your venture. You sell for $200.
Standard preference: I get $100, not $40, as my % would suggest, because I get at least every dollar I invested back.
2x preference: I get all $200, because I'm promised at least 2x my investment back.
Participating preferred: I get $120 (I think?) --- I first get my invested dollars back, and then I still get my % of the venture.