Do follow links allows to pass link juice from one webpage to another webpage. Do follow is one of the important ranking factor in SEO point of view. If do follow links or back links comes from other website then your website will improve in ranking. But we do not give do follow link untrusted website, forum, blogs,or other websites. Because it will low rank the website. Do follow link is very valuable link in link point of view. In web designing sites all the links are default by do follow links only. We only want to change the settings to no follow link. Do follow links can be followed by google.
Example of do follow link is <a href="http://www.google.com>Google</a>
No follow link does not pass link juice to another page. No follow link is used for untrusted websites, forums, social networks, etc. No follow link is not taken into account in page rank point of view. There is an advantage for no follow links. We cannot able to give do follow link for all type of links because it will loss our link juice then our website will not able to get high rank. For this type of problem no follow link was used. No follow links are not follow by bots. It can be understand by only human.
For examplle: <a href="http://www.google.com" rel="nofollow">Google</a>
Back links or Inbound links
Back links are the links which link to another pages of website. Back link is one of the serious factor in ranking point of view. Back links are very important in SEO because google wants more back links to give credit to the website. A website which has good number of back links will get high rank in SERP. Search engine will consider the content of the site to determine the back link whether the link is in good quality or not..If you are getting back links from other website then your content of your passage is good. Back links are the major metric factor for the ranking.
Social media links can be displayed on your website in different ways. Social links generally look like small square box symbols like Twitter, Google+, Facebook, Instagram, Linked in, etc.Social media links are important for the website because visitors are like to view social media so that they click on the buttons and they instantly redirected to social media. Social link is one of the ranking factor of SEO. Social link is useful for the visitors to go through your daily activities and follow them.
Broken links or Dead links are that no longer exist because the link which is directed to the website is removed by the user. Then it leads to page not found. If a website has number of broken links then it will low rank the page. Broken link make visitors that your is not trusted one. So you want to check the entire website whether it has any broken links in a specific piece of time. Broken links also formed by some of the users created firewall for their website to block links from other website.
Redirect link is a link that sends user from one url to another url. Due to some reasons we remove some of the url but we do not want loss link juice in the website. for this we use 301 redirect link. (ie) If we enter the removed url in the web address it will redirect to diferent url you have created. There is also an another type redirect is called 302 redirect. 302 redirect refers to temporarily moving it means if your site is under upgrade works but your visitor want to see your website then he will redirect to some temporary url. This type redirect is used for 24 hrs service websites.
Internal links are the hyper links which connect the web pages of the website in the form of anchor text or image. Internal links is very important in on page SEO. It is one of the important ranking factors. Internal links tell about the importance of every web page. Getting a link inside the website using anchor text as targeted keyword gives you high traffic to your website.