"来说"here is in the phrase of "对于……来说"， means “for (sb. or sth.)", "对于那些想看又买不起书的人来说" means "for those who like to read books but can not afford". "就是一 进街口靠墙的一个小棚子" means "it's a shed beside the wall at the entrance of the street (which you can see immediately) "

hi, I didn't login for several days, sorry for late response. In"一进街口", "一" means “as soon as”, the sentence actually means "as soon as (you) enter the street, (you can see) the shed beside the wall"