If you are in the U.S. this is absolutely the most important video you can watch. It very clearly details how the system really works, and why it is always bad to talk to the police without a lawyer present.
Note I didn't say, "Never talk to the police." You need someone with you that can understand the law and how work within the system. You never know when they might consider you part of the suspect pool. You can be helpful, just be helpful while protecting your own best interests.
One note about that video: he's updated his advice a bit. Our shitty Supreme Court has made "stay silent" a bit of an issue--it's safer to demand your lawyer instead.
It's not even about understanding the system, the presence of the lawyer forces the police to establish "scope".
If I'm just a witness, then the lawyer can make sure that what I say can't later be used against me for something unrelated.
If I'm a suspect, this prevents the police from going on a fishing expedition to just "find anything". Once they talk to the lawyer, they have to go hunting for "what they told the lawyer" as opposed to everything in the world.
https://youtu.be/d-7o9xYp7eE