How to know when to end conversations?

When talking to people, i usually get nervous because I don’t know when it’s appropriate to stop conversations and when to start new ones. I end up finding a way out of the conversation, which probably looks like I’m losing interest and am taking up another task. I’m too nervous to continue conversations because I’m afraid that I may be talking about the same topic too much and won’t be able to move on or that I’m talking too much in general. Additionally, I am unsure what to start new conversations about. I don’t know what topics are appropriate to bring up. I feel like I either come off as rude or as strange.