Internet marketing is the vast field. There are lots of way for doing online marketing such as
- SEO - Search engine optimization
- SMO Social media optimization
- Email marketing
- PPC and Display ad campaigns
- Youtube marketing
etc
A backlink is said to be of Good quality when it is coming from a site which is having high domain authority, very good amount of organic traffic, high trust factor (CF & TF by majestic) and moreover the site should relevant to your niche.
It is refer to online reputation management. It involves handling brand social media accounts and over all branding using various digital marketing techniques.
Yes, I think SEO is necessary for any website. Coder never develops any website SEO optimized. So, For better performance and online visibility, SEO is needed.
If you write content that focus on solving issue or problem of the user then visitors will automatically subscribe to your blog. All you need to write content that makes value for them.