Extension visa. I need to give them "境外人员住宿登记", what exactly is it?

I have student resident permit which will expire on 15 July, but I need to stay in China a little bit longer, so I need L type.
I went to entry administration bureau in order to ask about L type, they said that there will be no problems with making L type (but only for 1 month), it will cost 160 yuan.