What happens to my stocks if a company is delisted?

When a company is delisted, its stock no longer trades. However, you do still own the same percentage of that company. 
If the delisting is voluntary, it’s typically because it has been acquired by another company, in which case your shares will be transferred to the acquiring company. Alternatively, it could be because the company has decided to go private, in which case it will offer to buy back your shares for cash. 
If the delisting is involuntary, typically it is because the company has gone into liquidation, in which case your shares will have little to no value.