Tech cards are a unique type of card that you can play on your side of the board, which will render them at a specific place. They can have a range of actions that will happen every time your turn starts making them quite useful to overpower your opponent. Of course, there are cards that can destroy your opponents Tech.
You can view your or your opponents Tech when clicking on the small arrow on the right side of the board, just next to the planet. Each player can have 3 Tech cards on his side at all times.
To play a Tech card, simply drag it on your side of the board and drop it while an arrow hovers above it.
If you want to target a Tech, drag the correct card over it and release your mouse to drop it.