The summary of 来's usage, as a complement to user3306356's answer.
You can use 来 as a concrete verb, as in
奥巴马来北京见维尼熊, which you already know.
Less concrete it is when 来 is used in some verb serializations, as in
上来, the main verb is 过 or 上, 来 only functions as an indication of "towards me". Sometimes 来 is used metaphorically, as in
Even less concrete is in
让我来问一个问题吧. You don't literally "come" to ask the question, but 来 grabs your attention and gives you a sense of what is about to come. This falls into the 虚词 category.
In your example 来 indicates a purpose, and it also falls into the 虚词 category. If you think like a linguist, you can see the relation between "in order to" and "to come".
There are even less concrete cases:
这个人三十来岁。--来 means "about".
一来脑子好，二来动作快。——来 is put after a number to indicate that you are
我吃饭来。——来 is put after an action to indicate the past present tense. You
see 来着 more often, but sometimes 来 is also used.
八月里来桂花香。——来 means nothing. It's just a 语气助词. You use it to glue things together. It is less common in mandarin, but commonly seen in lyrics and some dialects.