Question
My lawn turned brown now I would like to know how to get it back green.

Answer
You dont give me much to go on.

Do you know why the lawn turned brown ?

Where are you located ? hot southern state or cold northern state ? How long have you had the lawn ? when did it turn brown ? Do you know the type of grass you have in the lawn ?

Southern lawns which consist of warm season grasses turn brown in fall (go dormant) and stay brown through winter. In early summer it will turn green automatically.

Northern gardeners may see the lawn turn brown due to very hot summers.

Lawns can also be destroyed due to lack of watering, due to over fertilizing, due to insect damage...

I really need some more information to help you determine if the lawn will green up on it's own, how to reseed (the timing and type of seeds to use depend on your location).