'Though' is a subordinating conjunction. It is used to connect an independent clause with a dependent clause.
'However' is a conjunctive adverb. It is used to join two clauses.

'Though' and 'however' show that something has happened in spite of a hurdle. To put it simply, they show the meaning 'but' and 'despite.' Watch:

'Though' can be placed at the beginning and the middle of the sentence. Note that 'though' introduces the contrast clause. When we use 'though' at the beginning of a sentence, the contrast clause gets a comma.
'However' can be used at the middle of the two sentences or clauses. 'However' also introduces the contrast clause or sentence. It is placed at the beginning of the contrast clause or sentence and has a comma right after it.

'Though' is informal and it is mainly used in spoken English. 'However' is formal and it can be used in both written and spoken English.