Title screen -> Learn to Play -> Tips and Tricks
or
binaries/data/mods/public/maps/tutorials/
The chevrons above the units' heads signify (from single to triple) basic, advanced and elite rank; they go along with increasing attack and HP values and decreasing gathering speeds. (Since this site's search function is phenomenally terrible I don't know if there's a good overview somewhere.)
Here on Medium AI (on Very Hard I don't outcompete economy early game, but I play quite intuitively, no videos or tips to know optimal build order, for now at least).