how https (SSL certificates) helps in website seo ?

Some of the benefits are from switching to HTTPS:-

1. Google has confirmed HTTPS as a ranking signal
2. Switching your website to HTTPS would increase your website visitors
3. It is important to say that it is not recommended to switch to HTTPS solely for SEO
4. If your website is new, it will give you a better place in the browser.

Some Extra Benefits are:

1. Better Rankings mean more traffic and visitors on the website.
2. Users like to trust in secure websites, not in "Not-Secure" websites.
3. Your visitors' information will be secured, as well as yours.
4. Stay away from phishing sites.

 

According to Stats-
1--84 percent of users will not purchase from a website without the security certficate- it can impact sales
2--Google definitely give you more power if you have a secure website- Google cares about a user security
3--Https is a ranking factor in Google's ranking factor since 2014
4- Site's trust is more important for user to carry out a transaction.

Google values trustworthy sources over anything else.

 

That's somewhat true now. Let's wait a year or two and recheck those rankings. I suspect Google will be moving aggressively to reward https pages and to delegitimize http pages. I just finished about two months of work to migrate my 430 http pages to https. I feel the effort will be well worth it in the times ahead.