U3

1.
All the time : I walk everywhere. (Pr.S)
Now: I'm doing karate. (Pr.Cont)

2.
I take medicine when I have a cold. Pr.S + when + Pr.S
I take aspirin if I have a headache. Pr.S + if + Pr.S

The zero conditional
http://www.e-grammar.org/if-clauses/
http://www.englisch-hilfen.de/en/grammar/conditional_special.htm
http://a4esl.org/q/h/vm/if-clauses.html
http://www.e-grammar.org/time-clauses/
http://www.kfmaas.de/gram_if.html