Ok the first example should be 'Do you want to do something?' and 'I want to watch a film', Apetecer in English means to feel like, or in colloquial British English, 'to fancy'. Tener ganas can mean to want, or also 'to feel like'. We usually use 'querer' for to want. So other ways to express this same idea Do you feel like doing something? Yes I feel like watching a film. Do you fancy doing something? Yes I fancy watching a film. All of these examples are acceptable, although 'to fancy' is a British expression, I think Americans would understand it from the context. The second example doesn't translate directly to English. If you ask in the present tense in English the meaning isn't the same as Spanish, you are asking how long you play each time you play e.g. How long do you play tennis? I play for an hour. It should be: How long have you been playing tennis? or How long have you played tennis? The answer should be 'I've been playing tennis for 8 years' or you could also say 'I've played tennis for 8 years'.. You don't use 'since' for this.

I agree with Paul's comments. I have nothing to add to his discussion about tennis. Americans understand "to fancy" as a British expression but we never say that. We might say- "¿Te apetece hacer algo?" "Si, tengo ganas de ver una película" Do you feel like doing something? Yes I feel like watching a film. Are you up for doing something? Yes, I feel like watching a film. "to be up for" - colloquial - apetecer, tener ganas de I'm not sure whether British folks use this expression.