I'm bored so I'll give this a go.
The first thing to understand is that fWAR is not tracking everything. Rather, fWAR is the coming together of several other tracking statistics to quantify the player's overall performance and its relative value to the team in an easily articulable number that most baseball fans understand, namely "How many wins was [insert player here] worth to his team?" That may seem like an impossible task on its face, however, statistical modeling has shown us that the results that happen on the field correlate to an expected value of runs produced, and that a certain number of runs produced is equivalent to a win produced. Some of the math has already been referenced here, so I'm not going to get into the details, but the importance of this point is that the numbers from fWAR do not represent "someone else's opinion" but an objective calculation of a player's relative value based on concepts that have met the rigorous standards of mathematical proof. Having studied mathematics myself, I know how rigorous those standards are, they make a prosecuting attorney's job in a murder case look easy.
Once we've established that fWAR is an objective measure, the next question is: what is fWAR measuring, exactly? I gave a rather simplistic definition earlier, but more context is needed. The name gives this context: fWAR stands for fangraphs Wins Above Replacement, which means that the value being measured is relative to a replacement player. This is where fWAR (and bWAR, because both use the same baseline for WAR) get into some assumptions that have certainly held up mathematically over time, but they are still assumptions, not proven, and therefore up for debate, though the evidence in their favor is strong. The theory behind this is that if a player gets hurt, that player must be replaced, and the type of player available to replace that player would not be a league average player, but a "replacement level" player, someone who is a free agent or currently on your AAA roster who will likely perform well below league average. Thus, the numbers that Fangraphs and Baseball Reference have agreed on are that they will assume that a team full of replacement players will produce a .294 winning percentage, or an average of 47.7 wins, leaving 1,000 WAR over 2,430 MLB games to be earned by the 780 players on MLB rosters at any given moment. Mathematical regression has shown these assumptions to be valid season after season, but that could change in the future. These 1,000 fWAR are currently divided up as 570 fWAR allocated to position players and 430 fWAR allocated to pitchers. Again, these allocations are supported by mathematical regression, but are subject to change in the future. The existence of a finite amount of fWAR per season can bring understanding to certain concepts like a player having a negative fWAR and illuminates the excellence of certain performances, such as Mike Trout accounting for ~1% of all fWAR in baseball for several years of his career.
Finally some things to keep in mind. Regarding relative value, fWAR is most appropriately viewed through the lens of ranges as opposed to exacts. For example, if Player A produces 4.4 fWAR and Player B produces 4.1 fWAR, they effectively produced the same value. If Player C produces 7.6 fWAR, we can conclude that Player C produced a great deal more value than Player A or Player B. That being the case, the question then becomes what's the demarcation point? The answer to that typically lies in the eye of the beholder, but 0.5 fWAR and 1.0 fWAR are good and fairly common ones, meaning one person could look at 0.5 fWAR as separating one player from another in value, where another could look at 1.0 fWAR as separating one player from another. Also, remember fWAR is a counting stat, akin to HR and RBI. This means the more opportunities a player has in a given season, the more likely they are to have a higher fWAR. This is why it is difficult for relievers and utility players to put up high fWAR totals, they don't get nearly as many opportunities as starting position players and starting pitchers. Thus, it is not likely the best measure of relative value of a utility player or reliever, whereas it is possibly the best measure of relative value of a starting position player or starting pitcher, and certainly is the quickest and most easily understandable measure of relative value of those players, hence the popularity it has enjoyed in the analytics community for some time now.
I hope this met the objective of "Please try and explain in a clear non-condescending manner as I am sure many would like a better grasp of this subject." If I wasn't clear, please ask any question, though I don't know that I'll have the answer, and if I was somehow condescending, that was not my intent.