Edited to add:
Our posts crossed so I've not addressed your specific example but I have dealt with a similar example.
Now read on to the original version
Thanks Chanah
I did notice this thread and was going to respond when I'd finished a previous answer. As Chanah says, it's a major area of study but I'll try and point you in the right direction.
Firstly some background but important points. The planets have natural significations that they always carry, though those may not be their primary meaning in a specific chart. You've already mentioned some of these with reference to Mercury and Communications. Be careful on the Moon and emotions, the Moon is really instinctive reactions. Think about some emotions and you'll realise the difference. Anger, Fear, Envy, Love, Sorrow are all emotions but you woundn't group them all together and say that the Moon shows them. You might prefer Mars for anger, Saturn for fear, Venus for love and most Astrologers do use those as significations for those planets. As well as instinctive reactions, there are other natural significations of the Moon, such as women as a whole, wife, mother and through motherhood, nurturing and protection. It also has signification of change and changeability, because of its phases.
Secondly, planets have
accidental signification, which simply means that signification that is specific to a chart we are looking at. This type of signification comes from where the planet is placed in the chart and also from what house it rules. So if you have Cancer on the cusp of the second house, the Moon has rulership of your finances and carries the special meaning of finances, for you. How good the Moon is at that role depends on its nature and its placement in the chart.
If for example, it was placed in Virgo in your fourth house, in a night chart, then the Moon is the triplcity ruler and has dignity both by triplicity and by placement in an angular house. It's strong. Your finances are also likely to be associated with fourth house issues, such as parents and family (you might work in a family business or receive an alllowance from your parents) or homes and real estate - so you might work for an estate agent or doing home improvements, or interior design. Whereever your finances come from you will handle them in something of a lunar way. They may be subject to ebbs and flows, (the tides are lunar) or you may guard and protect them, in a motherly fashion.
Placed elsewhere in the same chart, the signification might change a little. If the Moon is placed in Libra in the fifth, finances might be more related to children but you might not be as good at managing them, as the Moon has less dignity in Libra. Put the Moon in Capricorn in the eighth and you will struggle to manage those finances. The Moon does not 'like' Capricorn and performs with difficulty. What's more the eighth is a bad place to be, it's not aspected to the Ascendant (you) but it is opposed to the second (your finances). So those ebbs and flows might be accentuated by poor money management.
Chanah mentione a table of essential dignities, you will find one here:
http://www.hellenisticastrology.com/diagrams/planetary-rulerships-table.pdf
which you can download for future reference.
You mentioned transits. When the Moon transits a house/sign it brings both its natural and accidental signification to bear, though not necessarily equally or consistently. So you might have a range of significations that are possible if the Moon transits through your tenth house in Pisces. It will highlight income, which is clearly career related but it might have significations for your mother (a natural signification of the Moon and the tenth is the house of the mother) or your social and outward actions (which might actually require income to carry out). In Pisces the Moon has no dignity, it's peregrine, which means without dignity or wandering. So you might find it difficult to deal with financial issues during that period. Luckily the transits of the Moon are short, taking just over two days to go through a sign. This does not mean that they are insignificant, as some Astrologers seem to think. They may indeed be highly significant if they are also associated with other astrologically important events, such as directions or time lords.
Lastly, for now, you also need to consider other accidental dignities, including aspects to malefics or benefics, speed, retrograde movement, etc. This needs to be done both for the natal chart and for the transits.
There's a lot there and I've only given an outline. It will take you time to work your way through that and to get to grips with each step. So don't try and do everything at once. Work through, at your own pace, no matter how slowly. It will be rewarding but it needs time and patience. And, of course, feel free to ask questions