Ridgeline in Eugene is beginner friendly but heard the mtb section is currently closed for trail work. Check the map for open to mtb trails
Thurston Hills in Springfield has a nice green line Acer Spades. There is a group that rides there on Tuesday nites, Show up after 5 leave the parking lot at 5;30, (FB page- Eugene Mountain Bike Group). They will ride some trails wirh rocky tread (YewHaw)
Carpenter Bypass near Lorane is a network of trails, many are beginner friendly. I plan to ride there today, noon at North parking lot (gravel pile), I drive a green Tacoma and you are welcome to join me. Forum back if you plan to show.
Regarding riding fast , getting technical, and not falling, good luck with that. You’re new to mtb, learn to ride first, fall a few times, gain confidence then speed and tech…then fall some more.
I can’t show you how not to fall except for one thing, but I can show you all the local [close in] trails. Arlie has some great black diamond stuff. I rode Thurston today, always fun but smoke was bad, couldn’t take a deep breath. I ride often every week, xc style rider.