English contains an enormous amount of phrasal verbs. While the base of a phrasal verb is commonly shared with many others, the addition of a simple preposition can make it incredibly difficult for second-language learners to understand.
Come is pretty easy to understand, but the common use of come on doesn’t really involve movement.
Opposites aren’t always easy to understand, either. Get up means to awaken, but get down can mean to get off of a high ledge.
Learning about these differences can be pretty fun. But for those that need a little help, Easy Space Learning has a good reference at their site.
Image: Rebecca Pressman