يمكنني refer to the possibility of doing something هل من الممكن أن نستريح الآن is it possible to take a rest now ؟أيمكنني أن استخدم هاتفك may i(could i) use your phone استطيع refer to the ability يستطيع الطالب حلّ هذا التمرين بسهولة the student can solve this exercise easily

" انا استطيع ان افعل ذلك" "I can do that " in this in this sentence I understand that you are able to do x but You maybe do not want to do it right now or at least you are not willing to do so. in arabic both of them are almost the same!

يمكنني شراء هاتف لك في عيد ميلادك ، لكن لا أستطيع شراءها لك الآن