Fuses are used by the PICmicro® to set options like the oscillator type, watch dog timer enable, power up timers etc. The actual settings for fuse types are different from chip to chip and details for each can be found in the corresponding data sheets.
16F84 Example
The fuses shown should be WDT, PWRTE, Ocsillator and Code Protect.
If your project does not need the WDT enabled then click on the WDT list and select OFF or Disabled.
If your project does need the WDT enabled then click on the WDT list and select ON or Enabled.
Use the same method for the PWRTE and Code Protect fuse settings.
The Oscillator has 4 options available. If for example, your project uses 4MHz as the clock speed, then you would select HS from this fuse option.
When programming takes place this fuse data will be used to program the fuse register inside the PICMICRO© chip.
Please note that some chips after being code protected can no longer be re-programmed, so be careful.
You can also embed the fuse data inside the source code for your project. When MicroPro loads the assembled HEX file and finds fuse data, it will automatically set all the fuse options to match. See MPLAB® help for more details on CONFIG.