You may want to change your fluids, timing belts, etc if you don't know the history of the bike. Sounds like you will need to change and bleed the brakes for sure. The pedal runs the rear and right front caliper and the hand lever runs the left front caliper. They all may need a good cleaning. Find out which one is sticking first. I would change the clutch fluid as well and it is bled out the slave cylinder valve at the rear center of the motor and banjo bolt at the master cylinder. Wrap rags around that so you don't get fluid on anything, the fluid will eat things alive and melt plastic. There is plenty of help here so just jump on when you have questions. Welcome to the site! Paul
Not exectly sure what you mean by locks up. If you mean the wheel locks up when you put the brakes on, I would check for possible fluid leaking on the pads and rotor. That will cause the wheel to lock when brakes are applied.
If you mean that the calioer locks on and will not release, I would first try opening the bleeder and seeing if the brakes release. If it does there are 2 possible problems.. First, there is a tiny bleed hole in the master cy;infer. If this is plugged up with crud, the pressure cannot release. Second, the brake line may have collapsed. I have seen this with cars and heard of it happening on bikes. The pressure is allowed to pass when brakes are applied, but the collapsed line will not allow pressure to release.
If you put your location in your profile, you may find someone close by that would be willing to help out.