Broken thread in crank

Thread in crank damaged.
How to repair a torn pedal?
My pedal has fallen off, what should I do?
How many times have I heard the customer's translation ... "I bought a new bike and these pedals do not want to screw up at all ... One of them I managed halfway, but somehow it goes at an angle ..."
Let's leave the directions of screwing in and out of individual components for another occasion. Today I will only deal with the consequences of confusing them.
(or simple under-tightening that results in pulling out).