Review place value with your child. By this time, she should have a solid understanding of the "ones" and "tens" place when looking at a two digit number. For example, in the number 26, the "2" is in the "tens" position and the "6" is in the "ones" position.
Write a simple two digit addition problem on paper (you can use a chalkboard or whiteboard, if you prefer). Make sure that the numbers you choose do not have to be regrouped at this beginning stage. Children do not learn regrouping addition problems until second grade.
The equation should have the numbers stacked on top of each other, so that the "tens" and "ones" positions for the two numbers line up. See example here.
It helps a child when you label the "tens" and "ones" position above the problems and draw a line to separate the two columns, as shown in the example here. You may only have to do this for the first day or two, or once your child is comfortable with completing problems. Then you can remove the labels from all future problems.
Show your child how to add the "tens" column first, and then the "ones" column. Do one or two problems for your child to show examples. Now, let your child practice with your guidance.