Keep log in session on my website

I'm having trouble keeping a log session on my website. I have researched and tried many techniques in trying to keep the log in session on my website but to no avail. When a user logs in, I want the log in session to remain active until the user clicks "log off". Even if the user closes the browser and reopens, the session should still remain. I know google has something like this, even a website like [login to view URL] has this feature. At this time, when a user logs in, everything is fine but after about 30minutes to an hour, the user is automatically logged off. I want the log in session to remain forever, until the user manually logs off. I want someone who is skilled at php to help. You will need to read my current code and make necessary adjustments without ruining my website. Please no newbies, my website is not for training. The website is www.oyadance.com.