What is the difference between a co-ordinating clause and a subordinating clause?

A co-ordinate clause has equal importance to a main clause. For example, in "I ate a sandwich and Johnny ate pasta", the co-ordinating clause "Johnny ate a pasta" would make sense on its own. In this example, the conjunction "and" connects these two sentences together, so it's a co-ordinating conjunction. It makes a compound sentence.  In a subordinate clause, the main clause is more important and the subordinate clause would not make sense on its own. For example, "I bought a dress because it looked nice." The underlined part is the subordinate clause, and as you can see if you said it on its own, it wouldn't make much sense. Therefore, it needs the main clause, the more important clause (which is not underlined) in order for it to make sense. This is an example of a complex sentence.