Security :: Sessionid Usage For Logged In User?

I have a user login panel(called loginPanel1) standart from visual studio login control. 2 textbox 1 login button.

textBox1=UserName

textBox2=password

loginbutton1

I have a simple database table for user records:

Userid: int 4 key unique

username: varchar 50 not null

pass: varchar 50 not null

On user click to login button i query usertable from mssql usertable. If password is match i create a sessionid to try the user is verified temporarily for page. (my method can be wrong i dont know good the session and membership login session carry in asp.page)

When user pass is correct i open session with following code.

SqlDataAdapter adaptor1 = new SqlDataAdapter("select * from userTable where userName='" + Login1.UserName+"'", sqlconnection1);

...

(cleared long code)

filling ds with adaptor here
..

loginbutton1 click event:[code]....

There can be methodoligcal mistakes.

My question related to above is: 1. I have a sessionid (for example i set timeout 1 hour ) with above check. When user want to post a comment to a journalentry. How can i query that sessionid that earlier login page created, and how to deal with that sessionid to logically belongs to that user. I mean i have a sessionid per logged user that is obtained with checking from sql database to verify the user. But at next page (comments.aspx), when user wanted to post a comment to a journal for example. What should i do about that sessionid in comments.aspx's page "post comment" button event to check if that user is logged in. My question or my method can be wrong for user authentication about logins. I could not much find another method that easy level to log a user and carry the information about user logged in.

2. should i carry that sessionid with url (if i could manage to carry the sessionid to next comments.aspx page), how will i use it to ask like "that id is obtained by username snoopy" is username snoopy has logged in because there is a sessionid about that.I mean how to use sessionid when a user logged in with earlier page login.aspx that wanted to post a comment in comments.aspx. explain to useage of sessionid for login check i would appreciate. I checked some topics, some of them uses loginPanel of visual studio's automatically created database without any code behind. Others deal too complicated for user login info carry between pages.