I literally started playing this game 2 days ago and pretty sure this has been asked a gazilion of times so apologies but I can't seem to find the answer.
Each time I mine (mostly Dromi) I get a couple of minerals, as a result I have to vent the one I don't want. That turns mining into a real nightmare. Can this be automated or filtered to collect 1 type of material?
It seems there's lots of asteroids but really no map of where resources are, where to mine, where to sell. Saw a guy on YT had some website that helped I think but I can't find the video again. Do we have any tools mapping out the galaxy?
You can filter - but most people outside the starter area don't bother, they just fit a large enough refinery

. That contacts panel is on your left, btw - shoot off a few chunks, look them up on the contacts panel, then select what you don't want and put it to ignore. Yes, active collector limpets can make this difficult.
And don't forget that you've set something on ignore when you want to mine it later on...
Where to mine and where to sell - best tool for that is the
miner's tool. That's mainly useful for "new" mining, though (cores, surface deposits, subsurface) - stuff that shows up with a PWA and concentrates in hotspots. For classic laser mining, you'll just have to learn which type of rings holds which materials (or look it up - miner's reddit is usually a good place,
this post holds a table of materials and ring types). If you're asking for specific rocks in a ring, though, you'll need to contact the hardcore miners.
As for tools mapping out the Galaxy - two main sources, most of the remainder use one or the other of the two databanks:
EDDB (EDDN) and
EDSM. Another popular site is
Inara. And - since you've been asking - all the data in these sites was (and is) assembled and updated by players playing the game. If you play on PC (I think there's also a way for consoles, but you'd better ask in one of the console subgroups if that applies in your case), consider running one of the feeder apps, like
EDMC or
EDDiscovery, to help keeping the database up to date. Of course, that means that everyone else will get informed about that station paying prime directly next to a pristine ring - you can delay or switch off data tarnsmission, if you want to.