I have a anterior mass it is a 20 on hunsfield was 1.2 cm now 2.3 cm in size.it is anterior and on the upper pole of the left kidney. what does this mean?

It is best you discuss the report of imaging studies with your medical provider, then it would make sense to you in context of other informations that they may have about you. The information you have provided is not enough to tell you what is really going on though the mention of mass seems intimidating.

You did not say how long the interval of those CT scans are. If the CTs were without IV contrast, you need one with IV contrast. You are young so the mass should be at least biopsied or you should undergo a partial nephrectomy. Please follow with a urologist.