It's been 2 weeks since i broke my clavicle. is it advisable to walk & do sedentary, light tasks from the 3rd week onwards?

Yes: Avoid lifting or reaching above shoulder level until there are signs of healing on x-ray. This commonly takes about 6 weeks.

Yes: You should work on shoulder retraction, ice, stay away from nsaid's and do some light exercises that are non-painful. Isometric strengthening of shoulder rotator cuff muscles, shoulder retraction exercises and walking are good ideas to start with.