I have the Hotas Warthog without rudder pedals. How do I steer the aircraft on the grond and how do I use the brake. Once in the air how do I controle the rudder, is that the same as on the ground.

Should be able to steer with the rudder assignment. I normally have the brakes on the number 1 trigger button on the stick, which you should be able to assign pretty easily. Seems to work okay for most stuff although on taildraggers you might have to dab the brakes and keep the stick back to avoid nosing over. Normally you can gun the engine, apply a dab of brakes and rudder and a taildragger should swing around.

Welcome to Avsim!  I think Chock has given solid advice.  Ground handling can be done without rudder pedals, but I will say that once you try rudder pedals that feature toe brakes, you will always want a set of rudder pedals that allow the use of toe brakes.

THIS!! ^ What Stans says.

Pedals with toe brakes help a fair bit if and when differential braking is required 

There's a setting for "Take-Off Auto Rudder" under Settings - Assistance - Piloting. Despite the name, it not only allows you to control rudder with the joystick on takeoff, but it also allows you to do ground steering with the joystick on taxi. It's the same as the "autorudder" setting in FSX/P3D. I also have a Warthog and no pedals and that works for me.

By the way, I have to chuckle that two of the three responses to the OP's question of "how to steer/brake without rudder pedals?" were "buy rudder pedals." Ah, Avsim. 🙂 

James