For one thing, avsluta can never be used with the infinitive. You can say sluta prata! ('stop talking!'), but you can't use avsluta that way. I'm not sure we never use sluta with nouns, but at least I can say we usually don't. So I'd say Jag måste avsluta samtalet 'I must finish the conversation', but I wouldn't use sluta that way.
Thanks, these comments from forever ago are still so useful, wow. I think you mean to say avsulta can never be used as an imperative?
No, I meant that you can't use it together with another verb in the infinitive. You can use it with a noun, but not with a verb.
Avsluta samtalet! 'Finish the conversation!' = imperative + noun
With Sluta you can use it with a verb: Sluta prata! 'Stop talking!' – but you can't do that with avsluta.
Not really. You can use 'stop' with nouns too in English, like 'stop the train' but that is stoppa tåget in Swedish, not sluta.
And you can 'finish eating' which is sluta äta in Swedish.