I just found out a post that contains an answer and the answerer comments
Either you provide us with a screenshot/photo of the "MINUS SIGN" you're talking about, or I'm done helping you.
I do get that this is a rude comment and spills out the reputation of the site as a whole.
We have just entered public beta so shouldn't we be a little more of Helping nature to newer users?
The post is here https://elementaryos.stackexchange.com/questions/556/creating-partitions-for-the-elementary-os-installation
Note: I have flagged the comment.