Welcome

Basic sticky jump

A sticky jump is any jump assisted by the explosive knock back of the Demoman's own stickies. Compared to the Soldier's rocket jump, the Demoman pays more health, but jumps much higher and farther. This technique is often used to reach unusual locations on the map, cover ground quickly, bypass barriers, and surprise foes. To assist with sticky jumps, the Demoman has 25% damage resistance against any sticky he fires that does not damage an enemy. Critical hits do not deal extra self-damage or extra knockback to the Demoman, so they will not propel him farther. Any sticky jumping Demoman will display burning, smoky boots until he lands, similar to the Soldier.

To execute a successful sticky jump, place a sticky bomb on the ground and wait for it to arm. Jump over the sticky and detonate it. Your distance from the sticky's wide explosive radius will determine height, velocity, and damage taken to a significant degree. Crouch-jumping will cause the explosion to launch you significantly farther.

There are more advanced ways to Sticky Jump and if you want to continue the lessons we can go over the techniques. Extra techniques that involve specific weapons are-

Caber jumping-

The Ullapool Caber can be used to jump; by striking the ground or a nearby wall, the Demoman will be launched directly upwards, making it useful to reach some high locations. However, caber jumps are more damaging than sticky jumps or grenade jumps, and while easier, are not as effective. It is also possible to use caber jumps in combination with sticky jumps and grenade jumps; by striking a wall while airborne, the Demoman will gain a significant boost.

Cannon jumping

Similar to the Grenade Launcher, the Loose Cannon can be used to perform explosive jumps without the detonation of sticky bombs, or to retain the use of a charge shield.
While burning the fuse with Loose Cannon, fire a cannonball and jump at the moment as it is about to explode, while standing near and facing a wall, it will send you airborne. This can also be done while running and facing the ground, however the timing is tricky. If the jump isn't made with proper timing you will not achieve a high jump, and will only move a few feet.
While in the air, you can extend the length of your jump using the Chargin' Targe, Splendid Screen or Tide Turner.
An alternative way to cannon jump is to burn the fuse until the cannonball blows in the barrel, and crouch-jump in the precise moment of the blast, giving a more powerful boost. When doing so, the Demoman should aim approximately behind him, as the explosion of the cannonball takes place inside the weapon.

Rampsliding/Trimping

Rampsliding uses the charging ability of either the Chargin' Targe, Splendid Screen or Tide Turner to propel the player off of inclined surfaces.
Approach the incline you wish to slide off of at full running speed. You must not be stationary.
Jump and charge at the base of the ramp simultaneously. The steeper the incline, the closer to the ramp's base you must be.
Attempt to mid-air strafe sideways into the ramp (this is best done with the Tide Turner). Due to how the Source engine handles air strafing, you will gain a significant amount of speed.
If timed correctly, you will preserve all forward momentum and fly through the air while charging. Crouch and use the strafe keys along with your mouse to maneuver.

Thanks everyone and let me know in discussions if you want to begin lessons. Lessons are FREE! and same with rocket jumping lessons!

Bibliographies- https://wiki.teamfortress.com/wiki/Jumping#Basic_sticky_jump
Check out this page if you also want to learn more advanced techniques of jumping for demoman.