You can set up your match tactics from the Tactics link under the Squad menu. There are various instructions you can give to your players and the team as a whole, but before that you need to decide on which players are selected for the matches, and what positions they play.
In the Tactics page, you can see pitch positions on the right, where you can place your players. You can select 11 players in the starting lineup and 5 as substitutes. Substitute players can be introduced during the match via In-Game Changes which is explained later. Make sure there are no injured or suspended players in your line up.
There are 26 different positions on the pitch including the goalkeeper where you can place your players. Choose which player plays in what position based on their Position and other attributes.
Saving Your Tactics
You can save your current set of instructions using the Save button. Your Line Up, Formation, Team Instructions and Set Piece instructions will all be saved. If you plan to re-use the currently selected lineup, formation etc., you can use the Save As button and save it using a preferred name. Once you have saved it under a name, you can always load that using the Load button. And when you think you no longer need to keep a saved one, use the Delete button to delete it.
All unsaved changes will be lost when you leave the page, so always make sure you save your selections before you navigate away from the tactics page.
Tactics For Custom Matches
You can specify one of your saved tactics to be used during your custom matches rather than using the currently active one, so that you do not need to login before a custom match just to change your line up or formation. You can do this from the Tactics page by changing the saved tactics selected under Custom Match Tactics.