Adding letters to capacitor values isn't that complicated; it's just one more little detail to be aware of. The following sums up some basic letter codes for capacitor tolerances:
Some capacitors are defined by a three number code followed by a letter. This letter represents the tolerance of the capacitor, meaning how close the actual value of the capacitor can be expected to be to the indicated value of the capacitor. The tolerances are indicated as follows:
Read B as 0.10 percent.
Read C as 0.25 percent.
Read D as 0.5 percent.
Read E as 0.5 percent. This is a duplication of a D code.
Read F as 1 percent.
Read G as 2 percent.
Read H as 3 percent.
Read J as 5 percent.
Read K as 10 percent.
Read M as 20 percent.
Read N as 0.05 percent.
Read P as plus 100 percent to minus 0 percent.
Read Z as plus 80 percent to minus 20 percent.

The above was copied from this site, which adds a little bit more info.

Next week, we'll talk about more naming schemes, and wind up with a couple of links which illustrate just how (unnessarily?) complex this subject can become.

This is a tiny ceramic capacitor.  You can only read the stuff printed on it under high magnification

ceramic sapacitor01

Let's say that this is the same capacitor, but under high magnification. But what does '104' mean? Is it some kind of model number? Inventory number? Does it mean nothing to anyone but space aliens?

Ceramic capacitor

Nope. It tells you it's capacitance, in picofrads. The first two digits indicate part of it's capacitance value. The third digit indicates the number of zeros which follow the first two digits.

Thus, it's capacitance is 10, followed by four zeros, i.e., 100,000 picofarads (100,000 pF)

You can also just drop the last three zeros and call it 100 nanofarads (100 nF). Both are the same value; they're just  written differently.

You can find out a bit more here.

And even more, in a straight-to-the-point video, here.

This begins a series of posts about stuff which is printed on the outside of capacitors. We'll deal with some of the schemes for indicating mF, uF, nf, and pF.

For our purposes:

1 mF is also known as
one one-thousandth of a Farad
10 to the minus-3rd power of a Farad
0.001 of a Farad
1 millifarad

1 uF is also known as
one one-millionth of a Farad
10 to the minus-6th power of a Farad
0.000001 of a Farad
1 microfarad

1 nF is also known as
one one-billionth of a Farad
10 to the minus-9th power of a Farad
0.000000001 of a Farad
1 nanofarad

1 pF is also known as
one one-trillionth of a Farad
10 to the minus-12th power of a Farad
0.000000000001 of a Farad
1 picofarad

There are much larger capacitor values in other branches of electronics but we don't need to deal with that on a ham radio site.

Next, we begin relating the above definitions to the many codes used by capacitor manufacturers.
Meanwhile, there's more material about similar math notation on Wikipedia.

Appropos of nothing: there are also the mathematical prefixes Zepto- and Yocto-, which are not needed here. They just sound like two long lost Marx brothers. You know, Groucho, Chico, Harpo, Zeppo, Gummo, Zepto, and Yocto.