SEO is an acronym for Search Engine Optimization. SEO is the process of improving a website to rank better in the search engines. It's usually comprised of on-site and off-site actions.
On-site includes things like URL structure, content, internal linking, site speed, etc.
Off-site includes things like backlinks to your website, citations, etc.
This is difficult to answer accurately, because every business is different. Some business types are highly competitive while others aren't as much.
A good rule of thumb is 4 to 6 months before you'll start seeing improved results. But it could be as little as one month for local businesses and low competition areas.
PPC is an acronym for Pay Per Click.
It's a type of paid internet advertising in which advertisers are charged each time someone clicks on their ad.
For example, when you do a search on Google and see the top 2-4 top results with "Ad" next to them, these are PPC ads. If you were to click on any of those results, the owner of the website would be charged for your click.
Pay Per Click advertising is a good marketing strategy when you first start a website, and the SEO has not yet produced results. SEO can take a few months to start working, so, if you want visitors right away, PPC is a good way to do it.