What are the laws concerning picketing? I want to picket a company not giving a refund.
The laws vary considerably depending on where the place you want to picket is located. The federal constitution, and likely your state constitution, gives you freedom of speech rights to picket with certain limitations to protect the public that do not seem to apply here. An example would be if you wanted to picket to instigate a riot -- this action would clearly not be constitutionally protected.
Assuming the speech you wish to convey is constitutionally permissible, the local government (and state government) is permitted to regulate time, place, and manner considerations in the interests of public safety. Therefore, it is always a good idea to check with your local police department to seek if a certain permit is required or if the town has enacted an ordinance limiting picketing to certain times or places.
NOTE: This answer is not intended to be legal advice and should not be construed in that way. This answer does not create an attorney-client relationship and no such relationship may be created absent a signed retainer agreement. The author is licensed in Illinois only, and his answer is for educational purposes alone.