Mysz jedza chleb / Mysz jada chleb?
Why is the verb "Jada" present instead of "Jedza"?
You can say 'to eat' with two forms: 'jeść' i 'jadać'. "Jadać" means 'to eat from time to time'. So: ja jadam, ty jadasz, on/ona/ono jada, my jadamy, wy jadacie, oni jadają. "Mysz" is female, so: ona jada -mysz jada.
Myszy jadają (plural)
If you want to use the form: "jeść", it will be: ja jem, ty jesz, on/ona/ono je, my jemy, wy jecie, oni jedzą. So: "mysz je". "Myszy jedzą" (plural) I hope it helps ;)
The difference between "jada chleb" and "je chleb" is pretty much the difference between english "eats bread" and "is eating bread" (present simple and present continuous). Former means that the mouse "eats bread [from time to time]", and latter means that the mouse "is eating bread [right now]".
Although keep in mind that "mysz je chleb" can also mean "mouse eats bread [in general]", eg.
-Co je mysz? (What does the mouse eat?)
-Mysz je chleb (The mouse eats bread)