You don’t need to be worried about stammering when conversing with people. For a start, you don’t need to do all the talking.
Conversation is a two way thing.
Ask the person you’re talking with open-ended questions and let her/him do a lot of the talking as well.
One attitude I like adopt is that I’m talking with people and not talking to people.
‘With’ reminds me, that conversation is a balanced, give and take thing.