Quick answer
Х х = the ch in Scottish “loch” or German “Bach”. Never an English x, never a plain h.
kh
How to say it
Start to say “k”, then let the air keep flowing instead of stopping it. That hiss at the back of the mouth is Х.
Not an h
Foreign names with h usually arrive in Russian as г or х: Га́мбург (Hamburg), хо́бби (hobby). Which one depends on when the word was borrowed — there is no rule to learn, only examples.
In the middle of words
Х sits inside many everyday words: хорошо́, ти́хо, плохо́й. If you replace it with a plain h, Russians hear it immediately but understand you fine.
Typical mistakes
Reading Х as an English x
kh, as in “loch”
It is a single fricative, not k + s.
Saying хорошо́ with an h
a fuller, rougher kh
Close enough to be understood, but audibly foreign.
Check yourself
Which word contains Х?