"I do not run in the summer."
Translation:No corro en el verano.
So, I run ON Thursdays is: Yo corro los jueves, but I don't run IN the summer is No corro EN el verano. I was counted incorrect when I put Yo corro EN los jueves and wrong when I put No corro el verano. You really have to pay attention to the usage/translation of in and on. It's just a matter memorizing I guess. Spanish is like English...sometimes it doesn't make much sense.
As an adverb or a masculine noun, "mañana" means "tomorrow," "soon," or "the near future." When referring to "tomorrow," it generally doesn't take an article, though. As a feminine noun it means "morning."
So: "el mañana" = the near future.
"mañana" = tomorrow, shortly.
"la mañana" = morning.
"mañana por la mañana" = tomorrow morning.