[Jeb got stuck on the moon, how do I save him? This is my first Mun mission.]

Send a rocket with a probe and an empty crew cabin and try to land as close as possible to jeb (but don't crash into him) and let jeb walk towards the vessel. you can hold left shift to run, or use RCS jetpack. These things can help you go faster.

[Jets without air!]

It’s easy to stall on duna, there’s too little air, and you need wide wings to keep you in the sky. 

[Fighter plane design]

I think i can make a better engine by editing the config of the original engines, then i change its thrust and vector, as well as the flame color.  once i set the vectoring angle to 50 degrees and it burnt my tail wings off

[What did you do in KSP1 today?]

Bad luck i used time warp when flying a SR-71 blackbird at 20000m height. And when i swooped down at 1200m/s speed, the whole wing fell off and i splashed into the sea. The kerbals were alive but the plane was smashed. Do any of you have witnessed a plane torn apart at time warp*4? This is strange,and i lost 200000 in the accident!

[Fighter plane design]

I failed to insert an image, it has the body of F-14tomcat and the wing of Chinese J20

[Fighter plane design]

I designed a fighter plane with Airplane plus mod. Without afterburner, the thing can fly at 1.69 mach and with afterburner it can reach 2.46 mach. Is that fast?