Answer by "Hatem El-Nagar" is in standard Arabic. I suppose you're learning Egyptian dialect, right?
So, I'll explain usages and pronunciations in Egyptian dialect.
يكلم pronounced as "yekalem" mean "talk to"
بيكلم صاحبه
=beikalem sa7bo
=He's talking to his friend
يتكلم pronounced as "yetkalem" means "talk".
هو بيتكلم
=howa beitkalem
=He's talking
If you added عن it means "about".
For example:
هو بيتكلم عن صاحبه
=howa beitaklem 3n sa7bo
=He's talking about his friend
If you added مع it means "with".
For example:
هو بيتكلم مع صاحبه
=howa beitkalem m3a sa7bo
=He's talking with his friend
Note: If you saw يكلم is used instead of يتكلم , for example:
هو بيكلم عن صاحبه
=howa beikkalem (not beikalem) 3n sa7bo. (pronunciation is a bit different, we use it in speaking more than writing)
=He's talking about his friend.
And of course, you can conjugate both verbs with other subjects.
Hope this helps.