calendars in MS project

we have the same prob and i think in MS project we have two or 3 kind of calenders and i started to change the data in the options calenders and i started to change the hours per day and i put it once 8 and once 10 and once 24 while my original setting at starting the project was 10 hours per day for working including saturday and this mean 6 days per week and 60 hours per week and after i started to enter the activities he started to give me something like 1.8 one day and 80% of a day which mean i guess that the program took the next day as his default working hours as 8 and he divided 8/10 cause when i go to tool menu and options and calender and i started to change or to play with the values in working hours per day like this 24 he gave me 0.75 day which mean one day which mean i guess or according to my understanding he took 20 divided by 24 and it was 75% i really dont know for sure if somebody can explain to us or help us cause im new commer in this and this is my first action with MS project thanksss....