what do spies need what is the little sign thing

i am a beginner player

You need to build the structure first, then click on your colony to recruit the spy.

After you have done this you have to send a spy to a location, then once it has arrived click on the colony/relic or op where it is, next click plant agent. once you have planted the agent a little icon will appear on the bottom left of your spy's position, this is called spy infiltration, when you go to perform covet operations, every operation requiers diffrent amounts of spy infiltration.

Then perform whatever action you have enough infiltration on whenever you want