Any action performed by a bot requires energy. The energy can be spent on moving around, reproduction, getting more energy and many other things. A bot can also store energy for future use.
There are 3 ways of getting energy
1: Hunting using particle shots, also called Shooting. DNA command -1 .shoot results in a particle being shot in the direction the bot is facing. If the particle hits another bot, that bot will shoot back a particle containing a portion of its own energy. -6 shots will return an identical energy shot, but feed from the bot's Body points instead of energy reserves.
*.tiepres .tienum store -20 .tieval store -1 .tieloc store
Here the .tieval tells how much the feeding bot gets. The larger the magnitude of the negative number, the more energy the aggressor bot gets. There is a limit of 1000 for tie feeding. Note that positive values work as well, and allow you to give energy to the other bot. (Yeah, I don't know why either. Maybe you're a benevolent acetic?) Or perhaps the bot you were trying to feed from has just stored 1000 into your .tieval and is trying to eat you, as you eat it.
3: Tricking the target bot into sharing its energy with the aggressor. This method is similar to #2, but here you use the .sharenrg command. It is easier and does not cost any energy except to make the tie. Also, no waste is produced. However, you must wait for the tie to harden, giving your victim a chance to escape. The tie hardens in 20 cycles.
Bots can store energy as Body points with the .strbody command. It converts 10 energy points into 1 body point. To retrieve energy back from body, bots can use the .fdbody command. However there is a limit of 100 energy points per cycle that can be retrieved from body points.
Both strbody and fdbody (as with most other commands) take values in terms of change in energy. That is, how much energy to store, and how much energy to retrieve.