Post position problem

I think you also should give the URL of the website for really good help.

but it’s on my localserver

what is your theme? (download link?)

you probably need to totally change the way the loop is putting the posts out;
it is probably making rows of posts; you would need to change that to create columns.

hierarchy is like that
wrap div
header div
clear div
pagecontainer = it contains the post div’s
posts = width:250px and float:left give margin
clear
footer

[Code moderated as per the Forum Rules. Please use the pastebin]

this is index.php

this is the code of index.php
https://pastebin.com/v4PYqnYU