"The bread is at home."
Translation:Panis domi est.
Panis is the subject (nominative) form. It is used if we the bread is the thing doing the verb action or if it is being described using the verb esse ('to be'), here 'est'.
Panem is the direct object (accusative) form that is use should the verb action be performed on the bread.
Femina panem habet -> 'the woman has the bread' (the woman is doing the 'having' and is put into the nominative, the bread is what is being 'had', the thing the 'having' is done to so we put it into the accusative)
You can see similar form changes in English with pronouns.
'I see him' compared to 'He sees me'