I've already compiled and installed subversion,
now trying to add users to it.
And I find two articles on this, but they seem to be going in entire different direction.
The 1st is here, which looks very simple, and seems it's not necessary to create a user account(useradd ...)
the 2nd is here, which is a lot more complicated, and seems I need to create a user account for each svn user.
Which one should I follow?
The first thing you need to do is decide how your users will access the server. Either by svnserve, http (apache), or ssh. Once you have decided that then you setup accounts appropriate to the access method.
See the section in the red book about choosing a server. Once you have decide move on to the section about how authentication is handled for that method.
There's one line in the manual which helped me a lot when I read it. "If you absolutely need server-side logs of either server errors or client activities, an Apache-based server is your only option." When troubleshooting, I suspect you'll miss those logs if you don't have them.
In general, I've found that even with small teams, the effort to centralize user administration is time well spent.
You should follow systhread, which shows how to configure your svnserve server and allow access for remote users. This uses the svnserve server daemon, which is one common way to serve Subversion over the network. See The SVN manual for more information on this. You can also serve the svn repo using Apache webserver, and authenticate users using Apache and all it's power (LDAP, SSL, etc.)
linuxfromscratch discusses the unix user and group needed to run the svnserve server daemon. This may have been done already when you installed svn.