I created the first build on TC, everything is fine, it worked, I wanted to create another one with other files, in the same project I create another build, run it and it gets into the queue, and in the build itself it says:
There are no idle compatible agents which can run this build
What needs to be done so that an agent can perform several builds at once, or how to make another agent. In short, how to solve the problem, I will be grateful for your help.
TeamCity agents only run one build at a time and that's actually a good thing - your builds are guaranteed to be independent and you don't have to deal with the cache conflicts.
A common practice is to have a pool of agents to provide enough resources for parallel usage. The size of the pool is defined by your requirements, infrastructure capacity, and budget.
The agent setup process is off-topic for StackOverflow so I can only recommend to check out the official documentation on this matter.