Hi,
I am new in Linux Ubuntu and want to learn a bit. I have a question, it might be very simple for you. I have only "root" as a user in my system.

1. I want to create a new user called "user_1"
2. I want to create a folder called "project_1" in var/www
3. I want to give "user_1" R+W permisions to "project_1" folder only.
4. I want to do all these in "root@ubuntu:/home/ubuntu#" command line

Thank you in advance.

To create a new user you need to use useradd (see the help file to do it properly).
To create a folder use mkdir with root and use chown to change the propietary user of the folder.
Use chmod 666 /var/www/project_1 to change permissions (RW to all users).

If you want the user has access only to that folder, you must maintain permissions for other users.

Anyway all this can be found with a simple search in google/yahoo.

I use the man page or www.google.com/linux.

They are both handy.