You can click on your friend and visit them whatever they have a red hand on you can help them with what they need help on and you can revive trees by clicking on them and it ask you to ask for help to revive it or remove it

You have to wait for it to grow then it will produce 3 apples when you collect them by clicking on them it will produce more or the tree will die

You have to go to where the item is when you click on the paint brush, that's where you go to the place of where you first purchased one and it should say you have like '2 of these in inventory' or '10 of these in inventory' etc.