Permalinks growing with each new page created

p.s. I am also getting this error at the bottom of my permalinks page in WP Settings:

If your .htaccess file were writable, we could do this automatically, but it isn’t so these are the mod_rewrite rules you should have in your .htaccess file. Click in the field and press CTRL + a to select all.

It then provides a series of lines of code; but zip in the way of instructions as to where in the .htaccess file those lines should go.