I am trying to understand some of the idiosyncrasies of the English language. One is the use of double consonants. Why does the word bell have two letter L?
A handful of English consonant letters are often doubled when they come after a single vowel at the end of a word, especially in single-syllable words, or words that are stressed on the last syllable. The website "Logic of English" describes this:
We often double F, L, and S after a single vowel at the end of a base word.
If you follow the link, you'll see a list of many other common words ending in "ll"; this may help you to learn this spelling pattern. Note that it says "often" and not "always"; there are common words like "pencil" where the l is not doubled.
Here are other resources that describe this spelling pattern:
There are many other reasons double consonants may be used in English. For example, double "ll" may also show up when you add a verb ending to a word ending in a single l (explained here: http://www.dailywritingtips.com/one-l-or-two/; there is also a Stack Exchange question about it here: When is "L" doubled?).
Etymology often provides the key to questions like this. Etymology Online yields this:
Old English belle, common North Sea Germanic (cognates: Middle Dutch belle, Middle Low German belle) but not found elsewhere in Germanic (except as a borrowing), from PIE root *bhel- (4) "to sound, roar."
In the transition from Old English and Middle English into more modern usage, the terminal "e" dropped first from pronunciation, then from spelling.
(Chaucer fans will remember the journey that began in "Aprille," which we now pronounce with fewer syllables and spell with fewer letters.)
The monosyllable bell was once spelled belle. Exactly why it retained the doubled L while April did not may be as much a matter of 15th C printers' choice and London orthography than anything else. My guess is that the French word "Avril" may have had something to do with it.
Most of the rules on the subject have been created retroactively in an attempt to explain things that just sort of happened.