The hitpoint show your combat statistics of your health when you make runescape gold, which appear on the top of the screen.
The red of the hitpoint show how much you have lost in combat, while the green one shows your remaining health. You can select the 'statistics' menu to see the detailed hitpoint of cheap rs gold if you want to access to the accurate view of your health. This will display the amount of Hitpoints remaining from your total; for example, 18/45.
Always keep an eye on this and make sure that the health bar does not reach the bottom, or you will die! To avoid death, you will need to heal during a fight to restore your Hitpoints. For this you will need food. To see what food is 'best' and what heals the most to buy runescape gold, see the Cooking guide.
You can also run away by clicking on the ground before you die once you lose a battle. It is best for you to buy rs gold and keep moving once you retreat because the remained monsters may keep attacking you. If you run far enough away, monsters will eventually give up the chase.