On the estate, items can be gained from doing quests such as the Training - Equipment, you will also start with a full set of equipment in your inventory. You can also get equipment if you are level three by killing the skeletons behind the waterfall and looting the items they drop.
You can buy some basic equipment from an NPC on the Estate. The NPC in question is called Monty he can be found one square north of Guide Derwa on the same square as Patricia Preystalker and Vanessa the Healer.
Clicking on him will show the Sell items screen, this is for you to sell your old items to him … at the bottom is the Buy Items button click that and he will show you a list of all the items he is selling. He may have several pages of items so use the page buttons at the top of the screen to switch between pages.
Outside of the estate there are General Store NPCs (work the same as Monty), monsters to kill that drop loot, Quests to do that give special item rewards. You can also buy from players, vendors and from the Marketeer system. There is a Marketeer NPC at 31, 59.