Boss Laser has a list of starting points for settings on their site, with different values for different wattage machines: https://www.bosslaser.com/laser-settings
It won’t be perfect, but it should get you going.
For materials, Google is your friend - there are lots of online guides that will tell you what is safe, what is “mostly safe”, which materials don’t work well, and which ones to avoid completely.
In the never list, most prominent are PVC and vinyl, because they contain chloride compounds which turn into toxic and corrosive gas when burned. They’ll corrode the metal parts of your machine, kill you, and it’ll hurt the whole time you’re dying. (some people do cut these things, using very high performance exhaust systems and scrubbers)
Acrylic cuts well and is used often, but the fumes are bad for you, so make sure you’re venting outside.
Natural materials like natural woods, slate, leather, and felt work very well. Be aware that leather and felt smell to high heaven when burned (think burning fingernails and hair respectively), but they aren’t harmful.
HDPE melts and gets all over everything, polycarbonate resists lasing and mostly chars and blackens, and polystyrene has a tendency to melt and catch fire.
For metal marking, Cermark is kind of the industry standard, though it’s pricey. Dry Moly lube works well (though not quite as dark) and is significantly cheaper.