"上课"是一个词 is a word ,"上 课"中间有空格就是两个汉字are two characters

上课 is a word that first component 上 is a verb means to go and to attend and the other 课 is a noun that represents a type of meeting in classroom. Divid 上课 into two pieces, the 上 not only could express as a verb but also a prep utilized to present something is staying above something, and other types of usages. While 课 is a noun in a commonly use.

你是问这两个的意思有所不同？还是指词语的排列方式有所不同？

Hi Guy，are you able to share context of both words?

If these two are the vocabularies, they have the same meaning.