That’s good going!
I’ll leave the uber-nerds to answer properly but in short.
Bloodstains show where other players have died. If you’re online they’re likely to be recent real players. They can indicate dangers ahead or suicidal leaps.
Lighting a bonfire means you save. Sitting at a bonfire heals you completely and refills your Estus flask but will see all normal enemies, but not bosses, respawn. So it’s a trade off. If you don’t save and rest though and end up dying, you could lose a lot of progress. You can also Kindle a bonfire which does something pretty cool…
If you’re online, players can invade your game but only when you reverse Hollowing (your current form) and turn Human. To do that, you need to consume some Humanity. Then you’re open to be invaded but also able to ask players to help you out. I barely ever went human personally and stored up tons of Humanity and Souls, which in hindsight was a waste. But I was never really sure what being Human did other than allow some bored bellend to invade and kick your ass when you least needed it.