Hi Park, 

I have put all of your corrections in bold. One thing to remember is to always keep the same verb tense (past, present and future). Let me know if you have any questions.

There is a park near my apartment. It has a railroad track that runs from Yongsan to Paju .The train runs underground.  There is a park along  the railroad. The park which is near my house was opened last year. It had several long walking paths. It was covered with cement which was covenient for riding bicycles and taking  walks. When it was warm,  I could see cherry blossoms outside the windows. It was beautiful. I liked this cute park.