Hi, sorry I've been bit nosy about it but it is one of the conditions now that you must be over 21 y.o. to be granted entry clearance to UK as a spouse.
To your questions - try to look at these threads, they are about fiancee visa but generally are valid for the spouse visa as well:
Fiancee visa...
Letter of sponsorship
Also take a look at VFS web pages - you can find a lot of info there as well as on UK VISAS website.
And - last but not least - try to use "SEARCH" function in here - right side of that green banner near the top of the page. Or in here.
Good luck![]()