# in the day of trouble

"in times of trouble" or "when I have troubles"

# he will hide me

"he will protect me"

# his shelter ... his tent

Both of these refer to the tabernacle where the writer is worshiping God. 

# in the cover of his tent

The word "cover" represents something that hides and protects.

# He will lift me high on a rock

God keeping the writer safe from his enemies is spoken of as if God were placing him on a high rock where his enemies cannot reach him.