You/We/They will/shall be visiting. He/She/It will/shall have visited. I will/shall have visited. You/We/They will/shall have visited.

Is visiting or will be visiting?

I'm visiting is present tense, meaning you're doing it right now. I'll be visiting is future tense, informing someone you'll be coming to see them sometime in the future.

In which tense we use will be?

Many people consider will to be the present form (its past form is would), and like all present forms, it can be used to talk about the present or future. The “present tenses” (such as the present simple and present progressive) are also used when talking about the present or future (more on this below).