Create an OpenID at https://openid.stackexchange.com/
Go to you profile page (https://webapps.stackexchange.com/users/20021/loldop)
Click on the "my logins" link.
Click on the "add more logins..." link:
Select "log in with Stack Exchange" and enter the details created at step 1.
Optionally remove the existing login by ...
The creation / development of a web application is very broad topic and there isn't a site on the Stack Exchange Network which scope embraces all the questions about it.
If you are starting from zero look for an online resource like https://developer.mozilla.org/en-US/docs/Learn
If your question is about developing/administering WordPress try WordPress ...
All of the information that you need can be found in the Help Center, which is linked from the close banner message. At the link, you can find the following information:
This question does not appear to be about web applications within the scope defined by the community. What's on- and off-topic is not always intuitive, so it may be necessary to reword ...
Click the Star under the vote count for any question to mark it as a Favorite.
See also: How do favorite questions work?
Alternatively, every question has an RSS feed. The link is in the lower right corner after any answers. Just add that to your favorite feed-reader.
Click your user avatar at the top of the screen to go to your profile/activity page.
Click Edit Profile & Settings
Change your "Display Name" to the desired value, and Save.
(You need to do this from the full desktop website. You can't do it from an app or from the mobile web site.)