Categories, groups and lists of diffusion .. confusing

Simplify these tools and give docs touse them in most current providers
Its very difficult ti understand the interest of these three categories of tools!
Even correctly using one is difficult, choosing with one to use is a jumpp in a unknown world and understand how it interacts with your mail provider’s similar tool … a mess!!
So, please, simplify it (a unique list mecanism?) or at list give information on hok to use it with mains mails providers (at leat Gmail).

eM Client is designed to integrate well with Gmail, so, the categories are exactly the same as in Gmail.  But I’m not sure I really understand your issue.

Thanks for answering.
My problem is that I don’t want to manage categories + Groups + diffusion list.
I just want a mecanism with allow me to groupe pre existing contact in sets wich allow me to see theme and to send a mail to that set.
So far I understand eM, categoires does not allow that : just a way to have different presentations of contact not to send easilt a mail to a categorie of people; list of diffusion are not done with pre existing contacts, contact in a list can’t be adressed individualy. Groups, I don’t know what to do with.
Perhaps some explanation will solve my problem due to misundersyanding … but …???