You may wonder “how do the YouTubers make tnt cannons!” Well today the secret is reviled just follow these steps and you will have a perfect tnt cannon if these steps are confusing then look at pictures for steps the steps and pictures do not go together just follow pictures if you want to

1. Get these items: dispenser, tnt x 1000, any block, slab, redstone, repeater, ladder, water get at least a stack of all.
2. Place 1 dispenser facing you, one facing the right of you, and one facing the left of you. The first should be behind others
3. Place 5 stone on both sides of dispensers (touching)
4. Place water in the middle of dispensers
5. In the last two blocks place ladders to stop water
6. Last two blocks put dispensers 3 or more or less high (2x1 on both sides)
7. Put slabs on top of each block going diagonal each time the stone/block should have a slab on top dispensers too
8. Add a extra slab to make it 2 blocks long
9. At end of slabs put repeater
10. On all not repeater slabs put redstone
11. Connect redstone to one course
12. Place redstone on top of beginning dispensers so redstone all touce
13. Place lever in the middle of second dispencers
14. Place button somewhere touching redstone on beginning dispencers

Your done! Your cannon should look like the ones in picture
remember that to activate it press button first then 3 seconds later press lever the deactivate lever
your tnt should go flying! Ps. Remember to load the dispensers