i presume you mean in the app Pages.
go to FORMAT... STYLE... hit the advanced options tool... select CAPITALISATION and choose Title Case...
now go to write something and you'll see all the text will be Capitals, but if you turn your CAP LOCKS on, then you will be able to write in lower case but Pages will autocorrect the first letter of the word directly after a full stop.
Don't know if it will be much use to you right now, but I feel it's probably more use than some people (not naming names) on this particular thread.
Now I shall sprinkle you all with magic fairy dust love and stride off into the sunset.
xox