Sorry for the late reply. That is great to hear! I'm glad you got that figured out. The number next to the item in the inventory is the amount of it you have(you start the game with 100 trees). With the trees you can currently do two things: place them back down in the world where you want them to go, or use them to craft other items and blocks.
In order to place the tree back down, make sure it is in your toolbar where you can scroll to select it. In order to move the trees from the matrix of squares(the inventory slots) to the toolbar, left click on them so they are highlighted and then left click on the slot you would like to put them in. If you want to move the trees, or any item, one at a time instead of all at once, right click the slot you want the selected items to move to. Then when you are out of your inventory you can select the trees in your toolbar with the scroll wheel and right click to place them down in the world.
You can also use the trees to craft other items and blocks in the crafting menu, which is the group of 6 slots on the left side of the screen. The 4 slots forming the 2x2 grid are the ingredient slots, the slot with the hammer icon in it is the tool slot, and the last slot is the output slot. Move items into the ingredient and tool slots using the recipes provided on the Feed-X website homepage. Then the output slot will have an item appear in it. When the output item is taken from the output slot, ingredients used in the recipe will disappear from the ingredient slots, as they were used to make the output. Try out some of the recipes and let me know how they work.