Questions & Answers about Сегодня у меня лёгкий день.
Russian almost never uses иметь (“to have”) for everyday “have” sentences about yourself.
Instead, it uses the structure у + [person in genitive] + (есть) + noun:
- У меня лёгкий день. – I have an easy day.
- Literally: At me (there is) an easy day.
So у меня is the normal, idiomatic way to say “I have …”, while я имею лёгкий день would sound unnatural or overly formal/odd in this context.
Меня is in the genitive case.
The preposition у (“at, by, near”) always takes the genitive. That’s a fixed rule:
- у меня – at me
- у тебя – at you
- у него/неё – at him/her
In this structure у меня means “I have…”, but grammatically it’s literally “at me”, which is why the genitive is used.