Frequency Analysis

Read this:

Use the tool to determine the frequency of characters, bigrams, and trigrams of the text:

"Frequency analysis is the study of the distribution of the letters in a text. Analysis of frequencies help decrypting substitution-based ciphers using the fact that some letters apparitions are varying in a given language : in english, letters E, T or A are common while Z or Q are rare."

Then use the tool to determine frequency of chars, bigrams, and trigrams of this text:

"Iuhtxhqfb dqdobvlv lv wkh vwxgb ri wkh glvwulexwlrq ri wkh ohwwhuv lq d whaw. Dqdobvlv ri iuhtxhqflhv khos ghfubswlqj vxevwlwxwlrq-edvhg flskhuv xvlqj wkh idfw wkdw vrph ohwwhuv dssdulwlrqv duh ydublqj lq d jlyhq odqjxdjh : lq hqjolvk, ohwwhuv H, W ru D duh frpprq zkloh C ru T duh uduh."

Explain how frequency analysis can be used to identify the type of cipher used.