The bagpipes consist of a chanter (the melody pipe) 2 tenor drones and a bass drone.
Each “pipe” contains a reed traditionally made of cane but more often than not nowadays the drone reeds are made of synthetic materials- so 4 reeds in all.
The drones are tuned to the low a on the chanter. Tuning is achieved by changing the length of the drone by means of sliding the top section of each drone up or down.
This low is is a bit off of concert pitch of a which is 440Hz generally between 470 and 480Hz. The tenor drones are tuned an octave below the low a and the bass drone an octave below the tenor drones.
The chanter doesn’t follow a regular chromatic scale either each note is slightly off from a scale you would normally hear. This is to have a harmonic of each note in tune with the drones to achieve that sound you all love so much.
The overall sound is achieved by keeping the air pressure on all 4 (temperamental) reeds at a constant level my means of blowing into the the air reservoir (bag) then maintaining pressure with your arm between breaths. A task which requires a lot of practise to achieve as you have to also play the melody at the same time. This is where they get their reputation of difficulty from.
The whole overall sound of a well tuned and well played bagpipe up close is an experience not to be missed and I have personally seen people moved to tears from it.
Hope this answers your question