Hey,

where can I find the Nature Altar and do I need rune ess or pure ess?

It's north of shilo village. Graahk familiars take you very close, and so does the abyss. You also need pure essence. However, You shouldn't craft them because they give like 1 gp profit each and are abyssmal xp. I think fire runes or steam runes are a better alternative, but it's been a while since I've done low lvl rc training, so I could be wrong.

Thank you, is there an quest needed to come there?

Nope, but you need to do a miniquest to access the abyss.

Abyss? Miniquest? Tell me more!

http://runescape.wikia.com/wiki/Abyss_(miniquest)

Thank you, what runes will I get there?

Thank you, what runes will I get there?

The Nature Altar makes Nature runes.