PPC means pay per click and AdWords is a tool of Google to promote your business on web. you can create many campaigns in google adwords and run them to promote your business. these all promotion is paid you can choose many methods like Target CPA, CPC, Target ROAS, maximize clicks, maximize...
according to my experience, 200 visit's per day is sufficient to start google Adsense. To get this much traffic you should have good content on the blog or your site.
internal linking means to link your web page to each other.
Ex. if you are running a website and your product page link to the right product so its call a good internal linking but if your product is showing something else which is not related to what product name shoes that is bad internal...