Familiarize yourself with the alphabet. If your native language is Latinate, this will be very easy. If it's not, start with the basic sounds of each letter. There are 26 and there's a song to help you remember.[1]
Unlike many Germanic and Romance languages, English letters don't necessarily correlate with one specific sound (this is why English is regarded as one of the hardest languages to learn). Know that the vowels (and certain consonants in certain environments) have two or three sounds, depending on the word. For example, "A" sounds different in father, path, and say.