Gedmatch can be extremely bewildering at first, my reaction was similar to Sinann's - "I uploaded to Gedmatch, had a bit of a look around, backed out slowly and closed the door."
I still find little value in the 2,000 'one to many' matches they give you. The main value for me has been 'one to one', when I have been able to persuade an Ancestry match to upload there, or where someone has already got a Gedmatch kit number.
Jill, you ask "Another DNA question, if I may:- if I can persuade one of my 3 brothers to take the test, would it help my genealogy quest, given the addition of the Y chromosome? Is THIS where gedmatch comes in?"
Y chromosome is not looked at at Gedmatch, it is purely autosomal DNA matches that you will find there. However, your brothers will have inherited different DNA from your parents than you have, so could give you (if you manage or have access to their results) different matches, both at ancestry and elsewhere. My uncle inherited different DNA than my father - my paternal cousin has different useful paternal matches to me.
I suggest that, even if you don't fully understand it, you upload to Gedmatch and other sites - all bar ancestry has access to chromosome browser, ftDNA charge a fee for this.
Regards Margaret