есть is the infinitive form "to eat." ест is the present tense such as "eats" or "eating."
есть is also the word for "there is" like the sentence "у меня есть сестра" which translates to "I have a sister," or more literally "of me there is a sister."
In terms of pronunciation, есть has a palatized T sound and ест does not, but there is no difference in the pronunciation of есть as "to eat" and есть as "there is." You have to figure it out based on context.
I'm also having problems with pronunciation. With л, г, д, ш, щ, now I understand they represent l, g, d, sh, sh, respectively. But when "she" speaks they make different sounds and it's difficult for me to relate the corresponding sounds to their character. If there's any key or something to help with this issue I'd gladly accept it
As I understand it, it is pronounced like "a" when it, without stress, finishes a word.
Go ahead and say the word "about". Even though there is clearly the letter "a" at the beginning of the word, you probably pronounced it "uh-bow-t".
Now say, "A bout". Here, the letter is pronounced like "a" because it is stressed.
Words like яблоко and медленно seem, to me, to be good examples of this trait (also sometimes with a word as common as это, but not что-то, because both о's occur on a stress).