Rune Points are your energy. When using a tool or swinging a weapon you use Rune Points. How many Rune Points you have is shown by a blue bar below your HP bar.
Each weapon, tool, etc. have a set amount of RP usage that, when used, decreases the RP by that amount. It is pretty straightforward. However, the RP usage changes depending on your skill level and the level of the tool/weapon. For instance, if you have a tool that has a minimum level of 20, you are not recomended to use it until you are skill level twenty in that area (farming, fishing, magic, etc.). It will cost much more RP if you are lower than this skill level. If you are higher than the skill level, RP usage will decrease to a certain point, this point being determined by the level of the tool/weapon (normally around 7 RP). The bar at the top right that is blue shows rune points out of Five Hundred. If you are exuasted, RP usage is doubled, and if you have a cold, RP usage is Tripled. Foods can replenish the RP that you have. If you run out of RP, what normally uses RP uses HP instead. You CAN faint via using up all your HP with a tool/weapon, so keep an eye on the status bar, eh?
There are a few simple, basic RP-restoration strategies that you can use to reinvigorate yourself. Especially earlier in the game, these techniques are critical for assuring that you'll be able to do the things you want to do as the game-play unfolds.
- Meet Melody and open the Bath House. On your first trip to Whale Island, run all the way east in the first section until you meet Melody. Not only will you get the Cheap Hammer this way, but it'll open up the Bath House.
- Plant turnips on Whale Island immediately. As soon as the first day (Spring 2), plant ~3 plots of turnips on Whale Island. Once these mature, do not harvest them, just keep them there for the Runes. Every day, 3 plots on Whale Island will restore ~75% of your RP bar. Eventually, once other RP-replenishing techniques kick in, you can harvest the turnips and plant the off-season crops you want. Once the Green Ruins open, you can do the same thing there if you want/need to.
- Grow strawberries on your farm. The first time you visit Erik, shell out the 200G for the Strawberry Seeds - and when Lute arrives on Spring 7, buy the Kitchen and the Handy Pot. Growing and cooking Strawberries is a little more complicated than the Pickled Turnip approach that you see promoted everywhere, but it's way more efficient. Strawberries not only are a renewable crop, growing every two days (or every day once you're in prosperity), but they're only a 100G crop so turning them into RP instead of cash is a much better deal than expending a 210G turnip which takes 4 days to grow.
- Make Jam from the Cornucopia Tree Fruits. Foods restore an additional 25 RPs per level. So the Level 1 Strawberries we grow can make Level 1 Berry Jam (75 RP) for us or Level 2 Berry Jam (100 RP) if we're able to prepare it expertly. However, the level of the fruit from the Cornucopia Trees is determined by the type of hammer you have and whether you used the special attack - so, with one upgrade (to the Iron Hammer), you can collect up to Level 5 Cherries which will make Level 5 Jam (200 RP) or Level 6 Cherry Jam (225 RP).
- Go Fishing. Similar to the fruit from the Cornucopia Trees, the fish you catch will be at varying levels, depending primarily on the skill of your tool (the Fishing Pole). So when you catch a Level 4 Dye Trout, it can become a Level 4 or Level 5 Dye Grill (144 RP or 169 RP) or Level 4/5 Dye Sashimi (148RP/173RP), depending on your cooking prowess.
- Plan when you're going to Level Up. Killing a monster in a dungeon fight gives you experience. At certain thresholds, that experience will be enough to give you a Level Up - which is basically like a free trip to the Bath House. So, just like visiting the real Bath House, it makes sense to do it when you're nearly exhausted. Remember that if your own energy is too low, you still get experience points when fighting with a companion monster - so even if you're nearly wiped out, you can still have your tamed monster do all the fighting for you. Even if you have no weapons yet, say on Spring 5, all you need is a barn and a Pet Glove and you can start restoring HPs/RPs through battles!