How can I download apps to my Android phone using my computer?

How can I download apps to my Android phone using my computer and then transfer my pc to my phone....
Update: thanks all for helping me.Tell me one more thing it is also working if i didn't having internet access in my mobile.actually i having data card so that's why i didn't want any extra data pack on my mob. and u guys knowing better than me internet access much faster if i use through data card so plz help... show more thanks all for helping me.Tell me one more thing it is also working if i didn't having internet access in my mobile.actually i having data card so that's why i didn't want any extra data pack on my mob.
and u guys knowing better than me internet access much faster if i use through data card so plz help me....
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