A clunking sound in the front end of your car can be caused by a number of different things. It could be something as simple as a loose brake caliper or loose suspension components. Or, it could be something more serious like worn out ball joints or a bad wheel bearing.
If you hear a clunking sound when driving over bumps or turning corners, it's likely that something is wrong with your suspension. Check for loose bolts and components, and have a mechanic take a look if you're not sure what to do.
If you hear the clunking sound when braking, it's likely that your brake caliper is loose or damaged. Again, this is something that should be checked by a mechanic as soon as possible.
In some cases, a clunking sound in the front end can be caused by worn out wheel bearings. If this is the case, you'll usually hear the noise while driving at higher speeds. Have a mechanic check your wheel bearings and replace them if necessary.