Just add THE for spring.
"In THE spring, I often read or lie on the grass."
The second sentence is correct, however, the third sentence is not clear... what makes you relax?
In Spring, I often read or lie on the grass. Sometimes I play sports with my friends. THE GRASS. What (That's) a good place which make me relax.
Spring begins with capital letter.
Shuangyu,
Very well done. The 1st two sentences are correct. The third sentence is not clear. Where is the place that makes you relax? If you were to say, "The park is a good place that helps me to relax." it would be more correct. Keep up the good work.