How can I shall apply Tourist visa?

Have a good day. I want to go to China for travelling again ( 6 year ago one time I have visited in China). How can I shall apply for my visa ?There are so many people have tell me it is very difficult now for get Chinese visa. For my tourist visa need invitation from China ? I have not any people in China who will give me invitation letter. Now How can I get my tourist visa and which papers need requirement for me ? Please any people help me about my visa matter ?