Use components to build interfaces. Search the component's name in the Component panel (Shift + A) or use quick search (Ctrl + E). Once you added a Component to your page unlink it to make changes. Right-click on the symbol’s label and choose unlink from symbol. This is the rule. We use overrides only as an exception for simple components that you'd rather want to re-style on the specific page within Style Guide (buttons, toggles etc. - mostly atoms).
Footer is an additional bottom navigation for the website. It can hold links, company info, copyrights, buttons, forms and many other elements.