Let’s learn Japanese with manga. What you are going to learn on this page is:
今日はやる気がしない。もうやった。
今日はやる気がしない。
(I don’t want to do it today.)
今日（きょう）means ‘today’. は is a topic marking particle and does not mean anything.
やる means ‘do’. It is same as する. やる is often used in an informal conversation. 気（き）means ‘spirit’ or ‘feeling’. が is a topic marking particle and does not mean anything.
しない is the plain present negative form of する which means ‘not do’.
もうやった。
(I already did.)
もう means ‘already’. やった is the past tense of やる, which means ‘did’. You should know how to make たform which is same as the plain past positive form.