You can hear the short 'i' sound in words like pin, wish, and chin. Long 'i' sounds like its letter name, as in bite, time, and shine. One of the big phonics rules that kids learn to help them determine whether a word has a short 'i' sound or long 'i' sound is the silent 'e' rule, which says that a silent 'e' at the end of a word makes the vowel before it long. All of the long 'i' words above, for example, follow the silent 'e' rule.
Another helpful way to learn how to sound out vowels is to learn about word families, which are groups of words that have the same ending sound and spelling, such as pig, fig, and twig or fight, light, and sight. Word families teach kids to recognize letter and sound patterns, which helps them sound out words quicker and easier. If a child knows how to sound out pig for example, it's easy to sound out any word with the -ig ending. If your child is having trouble sounding out short and long 'i', try focusing on word families with the letter 'i'.
For extra practice, check out some of our vowel sound and word family worksheets, which I've linked to below.
I've also linked to a phonics activity that does a really great job of illustrating the silent 'e' rule.