Buying a house

How does that work? I'm only 21 so probably wont be able to get into one for another decade, but I like thinking ahead. The cost of living is low here so say I wanted to get a house that was like 180k, the rule of thumb is 20% right and you just pay off the rest with your mortgage? If you don't have the full 20% you can get a loan from a bank right? And how much will they loan you? It's probably not smart to get a huge loan, but I'm thinking 6% isn't bad. I really want to be into a house by 30 cause apartments suck.

I have 3 savings accounts, one for those big purchases around Christmas time or birthdays, second is for emergencies, and the third is for a house. I find that putting money into all 3 of them is confusing because I dont know which to prioritize. Each week I can afford to put $10 into each one, but should I be putting more in one than the other? I have about $40 in each since I just recently started saving (I'm disappointed I didn't start sooner)