How do i destroy someones hearthfire?
You have to have a sufficient amount of strength to do that (around 50 If I recall) and then just use the skill "destroy" on the H, tho it takes alot of time.
HFs are pretty hard to destroy for newbs.
Whats a pearl and how do i get them?
A pearl is considered one of the best curiosities in the game, giving a whoopin 18000 LP at full change in just 1 hour. You get them by boiling river mussels in a cauldron by a 1% chance.
Mussels themselves are found in shallow water. Generally, you see the mussels around 760 per*exp (eg. 19*40).
How can i get a sword?
With metal that you have to mine.
Obtaining metal is pretty hard tho

I suggest looking at Sevenless's guide about metal in the end :
http://www.havenandhearth.com/forum/viewtopic.php?f=2&t=19114Why is it i shot like 50 rocks from a sling at a fox and nothing happens?
Chance of hitting depends on the targets agility compared to your perception. Foxes have a high agility level

Where is everyone am i alone in haven and hearth?
The game world is MASSIVE ,and so the usual 300-400 people online at one time these days are spread out alot so finding another person is a pretty rare sight. Also players tend to avoid other players

HHs one of the main rules is to be paranoic all the time afterall.