I need to know that if off page SEO such as backlink building, web 2.0, blog commenting, forum commenting are still works for getting rank on google ? Please help me to understand.
Not really. Those links won't work for a few reasons: 1. Those have been highlighted by Google as spammy or "black hat" linking techniques 2. Those links, as well as other links from blogs, etc would usually have rel="nofollow" commands set up to prevent those links from being "counted" 3. Those are blog comments, the trust flow from these forum and blog posts would be low to start off with, so it's not worth the effort.
It still works but you need to be more focused while creating links, choose trustworthy sites for creating backlinks.
Yes if you can find dofollow links from forums and blogs they will still work, but most now a days have rel="nofollow" on. Remember to check the trust flow is matching yours before posting links.
It's still work but these techniques take time to make things done.You should have patience in yourself to see the result because the result appears almost after one week or two may be...
Maybe you should build fewer backlinks from authority websites, focus on building backlinks from social media instead, will create positive signals to search engine.
They are all old methods which most are no no-follow or even the do-follow links are usually very spammy sites, leading to your site getting penalty from Google for unnatural inbound links. Backlink building does work but newer methods are required apposed to the ones you stated.