At the bottom of each item, there is a box to enter your bid.

When you enter your first bid on gBay, you will be asked to enter your email address and entire home phone number. After you enter this information, you will not be prompted for it again.
Click Commit Bid to commit your bid to this item. To cancel your
bid, click Cancel Bid

After you have commited a bid, you will be brought to a screen confirming your bid.
Find out how to view items you have bid on