How do you build back link for website?

There are a few ways:

1) Build quality content that is valuable to the user. This is the best way to build backlinks, but it takes the biggest investment. If you have quality content, other quality websites will link to you.

2) Ask other websites to link to you. You can email them, but remember, they get tons of emails everyday. So you should find a way to provide value to them. The best way is to start a conversation with them via email, not necessarily asking for a link until you establish some sort of relationship.

3) You can submit your website to directories. There are tons of free directories out there, and several high quality directories that cost money. DMOZ is a free directory, and one of the best directories on the web, but it can be difficult to get into. Today, most SEO experts say low quality directories do not help with SEO, except for maybe helping your website initially get indexed.

Hope that helps. Best of luck!