States can make treaties and international organizations can make treaties. For example, there is a treaty between the UN and Cambodia to establish the special criminal tribunal.
What are treaties? Treaties are instruments that establish international rights and obligations. Treaties go by many names: conventions; memorandums, etc. at the root at ii if it’s a binding instrument subject to international law then it’s a treaty.
Where does the legal weight of treaties come from? Pacta servanta – there ought to be an obligation amongst states to adhere to their treaty obligations.