A tea press is similar to a coffee press (aka Infusion coffee makers.)
It’s a pot, usually glass, with a cover, and a flat strainer attached to a plunger. The flat strainer is designed so that it fits the sides of the pot very snugly, not allowing anything past the sides.
You put loose tea in the pot, pour boiling water on it, fit the strainer and plunger into the pot, without pressing the plunger down. You then wait the right amount of time for the tea you are brewing (e.g. 5 minutes), then press the plunger down. To make stronger tea, you can raise and lower the plunger a few times to swish the tea around.
The strainer traps the tea and pushes it down, leaving strained tea above it. The spout is at the top of the pot, well away from the trapped tea leaves at the bottom.
Many people swear by this method for getting optimum flavour from the tea leaves.
The downside, however, is that the leaves trapped at the bottom are still actually in the pot steeping, making subsequent cups of tea stronger and possibly even over-brewed.
To clean the pot, you remove the plunger, and then shake or wash the tea leaves out.