There are many ways of obtaining armour. Easiest I believe is to buy the armour from other players, specialty shops, or from the Grand Exchange. You may also get armour as monster drops. Stronger the armour, the harder the monster is. Last way I know of getting armours as a nonmember is the smithing skill. But it takes a very long to time to level up and cost you more for supplies than getting the armour itself. But members have one other way I know of obtaining armour I did not mention before. Treasure trails, these armours can be expensive, depending on which one you recieve from the clue scroll. There are three different levels of clue scroll. Each level increase becomes harder as you go up. Try your luck here for some rich looking armour or some good cash.