How do I read an RNA expression pattern?
This image shows the expression of a gene (in your case Lamin A/C) in various tissues. A picture with a higher resultion for mouse looks like this (from here): 


You can see the median expression (calculated from all samples) and can also see, in which tissues this gene is highly expressed and in which there is less or no expression.

This is important if you want to analyze the function of a gene. The tissue specific expression pattern can vary strongly between different tissues (as you can see in the figure) which can give information about the function of the gene. The same is true if you look on the time distribution of gene expression, you can identify genes which are important for different steps of differentiation.