Since there is no distinction between present and future tense in Japanese, you will ultimately have to figure out which one it is on your own. Luckily, it isn't too difficult.
Here are some tips.
1. Look for other words that could suggest that the action will happen in the future. Words like tomorrow, later, next year, etc are obvious indicators of a future action.
2. Look at the surrounding context. Is someone asking a question about something that has been planned for tomorrow? Are you talking about tonight's plans? Then you're probably talking in future tense.
3. Does the sentence make sense in present tense? If not, it's future. Remember that present tense in Japanese is not equal to present progressive in English (i.e. I am eating. He is walking.) In fact, Japanese present tense is the same as that of English. ケーキを食べる (if we assume that "I" is the subject) means "I eat cake" or "I will eat cake." However, if we ask someone what they want to eat later, it wouldn't make much sense to respond with "I eat cake." We would say "I will eat cake", right?
It's easier than it seems. If you keep reading/listening to Japanese, I'm sure you'll quickly be able to tell the difference. :)