To move to the start of a line use C-a and to move to the end of a line, use C-e.
To move to the start or end of a sentence, use M-a and M-e respectively. Note that by default, emacs assumes sentences are broken up by a full stop and then two spaces. If you want it to recognise full stop followed by a single space as the end of a sentence then add the following to your emacs config file:
;; sentences end with single space (setq sentence-end-double-space nil)
Note that this will lead emacs to get a bit confused about abbreviations e.g. that one just there.
Pragmatic Emacs 