Start with a really small rocket, and make it work. Then build a larger stage under it and tinker with that until it works. Then add another stage. Repeat until it reaches whatever your goal was.
Some posts have been trimmed from this thread. Please keep in mind that this forum attracts many younger visitors, and we'd prefer to avoid talking about 'adult content' such as liquor (2.2.c).
Somewhat overlapping what others have said: as the craft starts to lift off, it may end up riding the front wheel as a unicycle and start wobbling. Applying some pitch-up as you roll down the runway can prevent that.
The thing to do would be to ask in the thread for whatever mod this part comes from.
And since the Tutorials section is for offering help rather than asking for it, this thread will now be closed.
Squad made the game, but Steam is a separate company which operates forums. Squad does not control Steam. Please make suggestions about the Steam forum on the Steam forum, because we here can't make changes there.