Trade is an important part of the road to success. If you use some time finding the right players to the right players you can earn a good amount of Credits. However, this requires you know how the market works and know which types of players are in high demand.
To buy a player you must find him first. This is done via "Player Search" (Trade > Player search). When you've found a player you want to buy, select "Choose action" > "Place bid" in the upper right corner of the player profile page.
When you place a bid you must define a "bid" and an "auto bid". Bid is the amount of Credits you want to bid for the player. Auto bid in the maximum amount of Credits you want to spend on the player. This number is hidden from the seller. If you bid is accepted an auction starts. Should another club place a bid that is higher than your bid but less than your auto bid the system will automatically outbid that club.
After the seller has accepted your bid and hereby started an auction, this auction can be monitored via Trade > Bids > Auctions. On this page you can also increase your auto bid and monitor the amount of time there is left of the auction.