Yes, 75% is the pass mark ... pretty high, in my opinion! But don't worry, Grace ... you'll GET THERE with plenty of practice! And you'd be surprised
at the number of British subjects who've scored considerably lower than YOU did when THEY attempted it ... myself included, I'm ashamed to admit!
The Test can be taken at any time during the valdity of your Spousal Visa ... but it is obviously advisable to wait until you've BEEN here long enough - say, at least a year - to acclimatise yourself to our way of life. By the same token, though, you should not leave it too close to the date(s) that you're due to apply for ILR.
The Test itself, consists of 24 questions ... SOME of which are of the 'Multiple Choice' type - whereas OTHERS require examinees to tick whether certain statements are 'True' or 'False'.
I hope I've been able to give you some idea of what is involved.