sorry.. the answer is probably really obvious but how can I search threads?

In the lower left corner of each thread there is a search box in which you can type a word or phrase and then click on "Search Topic".

Thanks- can i search more than 1 forum at a time?

Here you go: Help - Search Threads

At the top of every page there is a search bar. Also you can use the forums only search on the right side of the member menu bar .

My favourite is the advanced search feature under "Forums Search" because of all the filters.