Look at the ending of the noun. If a noun ends with a consonant, it is masculine. Female end in a, neuter in o. There are instances where Female and Neuter nouns end with other vowels, but think of this as a rule of thumb to begin identifying gender.
There is a different meaning of the word план in Russian. It means - marijuana. Of course this is slang. So if You had put on a table a matchbox and said "Here's our plan" someone can think about marijuana. https://youtu.be/oZCRHTaDwdE