When you buy a home, you have to put down a deposit.
Typically that deposit amount is 3% of the purchase price of the home.
Keep in mind that this 3% amount is not set in stone, but it is customary.
You can put any amount you want, however the seller will not think you are a serious buyer and probably won't accept your offer unless you put at least 3% for your deposit amount.
You have to send your deposit over to the escrow company to hold within 3 days of getting your offer accepted.