Know-How Exchange : Advertising/PR

I want to know the basics of advertising

The "best form of advertising" depend on what you are selling, who you want to sell it to, and what type of response you want to receive from your advertising.

This is a broad subject that can't be covered quickly in a forum such as this. Here's some links that will get you started:
https://www.startupnation.com/articles/1095/1/AT_How-to-Start-Advertising-y...
https://www.entrepreneur.com/advertising/howto.html
https://www.managementhelp.org/ad_prmot/ad_prmot.htm
https://www.knowthis.com/promoadv/basics-of-advertising-and-general-ad-info...
https://www.allbusiness.com/marketing/advertising/1417-1.html

Inbound Marketing.

https://blog.hubspot.com/blog/tabid/6307/bid/2989/Outbound-vs-Inbound-Marke...

Advertising is a very broad topic. I'd recommend the following books:
--> David Ogilvy - Ogilvy on Advertising
--> Al & Laura Ries, Jack Trout - The 22 Immutable Laws of Branding, The 22 Immutable Laws of Marketing
--> Luke Sullivan - Hey, Whipple, Squeeze This : A Guide to Creating Great Ads

Each of these 4 books provides their own "basics", and each has its own special set of lessons.

Beyond that - the advertising that is best is (as Ogilvy says) the one that works. So, that is very dependent on where your target market is, and how they would use your product. If you are selling things online, then advertise online (search ads, banner ads, inhouse email list, etc.). If you are selling things to businesses, then send them direct mail. If you are selling "fad" products to young people then advertise in movie theaters or in video games.

Alongside the placement and media of the ad, you will also need great copy and creative. The copy and creative does not need to be award winning. It needs to make people take action: visit your website, call you, come to your store, and so on; have a look at your product or service; and buy!

Hope that helps.
Dave