However

I see a lot of sentences that start with 'However' but my understanding is that it must relate to the current sentence. I would write 'I see a number sentences that start with 'However'; however, my understanding is that it must relate to the sentence it is in, be preceded by a semicolon and followed by a comma (I believe this sentence to be correct). However, my thinking may not be correct (I believe this sentence to be incorrect).

However we write, it needs to be comprehensible (I believe this is an alternative acceptable way of writing).

Please advise.

Many thanks

Dave