Japanese, East Asians commonly make a mistake in this area.
As an adjective, "most" means "the majority", "largest part", or "nearly all." For example:
1. Most cars have four doors.
2. Most people would like to be rich.
We can also use "most" as a pronoun, with a similar meaning:
1. Most of my friends can speak English.
2. I spent most of the $100 you gave me.
"Almost" is an adverb. Its meaning is similar to "nearly".
1. I almost failed the exam. (But I did not fail).
2. The hotel was almost empty. (There were only 5 guests.)
3. Almost everything was destroyed in the tsunami. (But a few buildings stand).