Your Question its to wide and general (add screenshot or some code + Theme name).

For start see this docs:
http://documentation.concrete5.org/developers/concepts...
http://documentation.concrete5.org/editors/dashboard/pages-and-them...

In general:
Step 1- Find the homepage template:
Site map --> one click on "home" -->Design & type

Open Modal: You see for example:
Page template: right_sidebar
Page type: Some-page-type

In other words the page "home" use [Temple]: right_sidebar.php located inside theme root folder (Test: write inside this file "hello-world" and see the change in your home page)

Step 2:
Change this template to full (full.php) template (or any template you want). If you dont have full template you must create this layout.
______________________________________________________________________

Grid in general control the responsive layout (with/without container + rows + cols) **!! not SEO or composer**
LTR sites:
Left sidebar:
3 col - 9 col

Right sidebar:
9 col - 3 col

Full:
container (or 12col)

Look at this for example (or endless examples in google)
https://getbootstrap.com/examples/grid/...

super, clearly explained, and it is working !!

thanks !