Welcome Marylin! Sounds like you have a good start with your mother's collection. Where to start? I think a great place is downloading, printing and working with the One Stamp for Every Country album. It is a great overview and introduces you to the possibilities.
You can download the pdf file for the album here. Use some heavy weight paper ... i.e. 64lbs or so. If printed on both sides, the album will fill a 2" 3-ring binder. It is a fun exercise to get started.
http://stamps.org/userfiles/file/al...-Country.pdfor
http://postalmuseum.si.edu/stampgal...ryalbum.htmlFor further discussion, go here:
https://goscf.com/t/50496&whichpage=-1To learn about specific stamps, try here:
http://www.stampworld.com/en/This site might also be helpful:
http://www.2-clicks-stamps.com/arti...lecting.htmlAnd of course this is one of the best Canadian sites:
https://www.rpsc.org/