what is the difference between component.get("") and component:find("")?

I thought component.get("") was for aura:attribute and component.find("") was for lightning:input but if on my client-side controller I do component.get("") with a lightning:input, I get an error, the page doesn't load itself.

I read the documentation (https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/js_cb_find_by_id.htm) but I don't understand.

This is my example:

lightning:input aura:id="salutationTest" label="Hello" name="hello" value="hello"

The page doesn't load itself and I have no error message.