First of all welcome, some men make the most wonderful cake decorators! Well, a crumbcoat can be different things. But mainly it is something that seals the crumbs to the cake so that when you ice the cake, the crumbs don't break off into the icing. So basically you get a more professional finish.
Most people here use their buttercream icing to crumbcoat, but they use it fairly sparingly. You wait until your cakes are completely cool before crumbcoating with buttercream. Some professionals put almost no icing on, you can almost see through the crumbcoat, others put it on heavier. Generally you are better off sticking with using the same consistency of icing for your crumbcoat as you use for your final icing coat. If you thin it down with more liquid than your regular icing and you normally use water in your icing, the final coat of icing can try to absorb some of the crumbcoat moisture and this can result in cracking of your icing. I use milk and cream in my icing, so it isn't an issue.
So you let the crumbcoat set for about 25 minutes or so, some folks refrigerate it, I don't, then you apply your final icing.
Another method is to heat apricot glaze and apply it to your cakes once they come out of the pans or once they are cooled. You use a pastry brush and gently and sparingly brush the warm glaze on the cake to seal in the crumbs. You let it cool completely and set before putting on your icing.
Your crumbcoat not only seals in the crumbs but it also seals in the moisture allowing your cake to stay fresh and moist longer.
Hugs Squirrelly Cakes