Ability is simply the number at the end of the name of each ability;
From left to right you have Growth (+36 for example), the name of each ability (Bomber, for example) and ability, which for the bomber stat on this pilot is 2624.
To calculate true ability, you also need to look at the sailors manpower;
From left to right you have Rookies in red (which increase true ability by 0 each), Experts in white (which increase your true ability by ability x1 each) and Veterans in green (which increase true ability by ability x4 each).
If you're wondering why rookies dont ADD any ability themselves, this is because what they actually do is require you to fill a sailors manpower to achieve full ability, since any lack of recruits lowers TA.
To calculate TA is simple. Multiple your veterans by 4 and add the number of experts to the result. For the above example that is 100x4, which is 400, then +264, so 664. Then you multiply that number by the sailors ability. So 664 x 2624 means my bomber here has 1,742,336 Bomber TA. Simple really.
It gets more complicated if you have a sailor that doesnt have full recruits (if you were trying to save weight or trimming a BO to calibrate your lines to match your range). So here is an alternative method;
Look at the sailors recruit window, and add together the percentages list. So, I have 65% from Veterans, 39% from Experts and -41% from Recruits. That gives me a total percentage of 63%. Now, I multiply that by the max manpower, so thats 0.63 x 866, which is 545 and that is the number I multiply by the displayed ability (which for my example SN BO is 2627.
Arguably, this method is slightly longer than the first, but it takes into account the negative effect of missing recruits.