Making first post wider than other posts on home page(default)

you create a variable that holds the count of the loop. then with every iteration you increment this variable.

in your loop you can check for the first post to do something else then the rest of the posts, assign a different css class for example.

// create var for count
$count = 0;

// do your loop & increment the var
if (have_posts()) : while (have_posts()) : the_post(); $count++;

if ($count === 1) :
// do code for only the first post...
endif;

// do code for the rest of your posts...

// end loop
endwhile; endif;