Western script letters are derived from Egyptian hyeroglyphics
D.Anton
Egyptian hyeroglyphics are logograms, consisting of signs with meanings and sounds whose role is to clarify the meanings of the texts. From the original Egyptian hieroglyphics a diverse variety of simplified scripts developed.                                                                                 Hyeroglyphics

The demotic writing system (also Egyptian) was generated as a simplified version of the hieroglyphics system.
This one in turn evolved into the Coptic script (today the religious language of Egyptian Christians). This process led to the creation of simpler signs from the ancient hieroglyphs.
At first these symbols identified consonant and syllabic sounds to which additional marks were added to define the vowel sounds.
Many written languages ​​based on hieroglyphs or logograms evolved from a conceptual representation (ideographic: each sign equals an idea) to phonetic systems (each letter represents a sound). At first signs represented syllabic sounds. Later each letter became a consonant sound and vowels are represented with markers signs (vowel markers). Finally, in some systems (eg Greek) independent vowel signs developed (alpha, epsilon, etc) which were also used in modern European alphabetic systems (Greek, Latin, Cyrillic).
An example of this development is observed with the evolution of the letter aleph which is derived from two hieroglyphs, a sign depicting a bull and another representing a vulture. The Phoenicians  took the logograma ox in his writing (Aramaic) as syllabic symbol (representing in this case a "glottal stop" or glottal stop), to which it was added an associated vowel. The Greeks, whose language did not have a glottal stop, transformed it in the "alpha" vowel. In the Latin script it became the letter A.
            The symbol "beth" began with a logogram representing a house, then it became a symbol of a consonant sound "beit" or "beth" in Aramaic and Arabic respectively. In Greek it was renamed "beta" and later was rewritten as "B" in the Latin script system.                Demotic script

In the same way the symbol "daleth" (door) became the Greek and Roman "delta" and "D" letters. The logogram sign for "gimel", which meant "camel" was at first an ideographic image of a throwing stick. Later it became a  onsonant symbol. The Greeks retook it as the letter "gamma" and Romans represented by the letters "C" or "G".
The monosyllabic word "He" (which meant "window") originally was the image of a man with his raised arms calling for prayer. The Greeks transformed it into "epsilon" and Romans into the letter "E".
With other letters similar processes occurred. The evolutionary end result was the Greco-Roman system (which includes as a derivative the  Cyrillic script currently used in Russia and Ukraine).

Phonetic symbols of consonants in the Arabic, Hebrew, Syriac (Aramaic) and Greek scripts