I have poor communication and social skills, which is the cause that at the age of 20, I still don't have a close friend. How can I improve my skills?

It might help if you took the focus off yourself, is there anyway you could volunteer at an animal rescue centre. Talking to others about the care and wellbeing of animals, and helping to care for them. You will meet lovely people in that world that know what unconditional love and kindness is. Good luck.