No problem - you can do this easily, like "point and shoot".
Where you want the total, just type =, then click on the cell containing the first value to add, then type a +, then click on the second cell to add, (even if it is on another worksheet - just navigate to it and click the relevant cell), to finish just press enter.
The resulting formula will look something like
where A2 is a value from the first worksheet, and B6 is the value you want to add from the second.
By the way, the program name is Excel, not XL, helpers usually search for posts to reply to relating to their expertise and experiences.