Oscar the Grouch's greeting?
Does Czech people really use such construction in conversation? Or it is just a phrase?
Not often but I guess you could use it for example if you expect some unpleasant work in the afternoon.
I'm still kinda confused by the use of accents?
Accent is almost always on the first syllable of the word
I am quite sure LorriAbleC meant "diacritic marks" when she said "accents". Most foreigners call them accents even though only some diacritic marks can be called as such (čárka yes, háček no).
If you mean the diacritic marks on some letters, like é or ž, all you have to do is to read the "tips and notes" section on the first skill, where they explain the letters and their sounds.