You use these as a last resort. If you can rewrite your sentences without using colons or semicolons, then you really should do that. Yet if you must... use colons to "introduce" something, and use semicolons as something stronger than a comma but weaker than a full stop. Any problems? See my comment above about rewriting your text more clearly.

It is use in combining two simple sentences. When two independent clauses or simple sentences are combined, we can use AND, BUT and, OR. :)