Sometimes when using SSMS you will see a redline under a table or object name in your T-SQL. This means SSMS thinks the object doesn’t exist in the current database. Usually it’s right, but if you have just created the object, the query editor wont know as it’s local cache is not regularly refreshed. To force a refresh you can hit Ctrl + Shift + R but I always forget keyboard shortcuts. For this I like to add a button to the toolbar.
This is a good intro-level article on SSMS basics and some configuration options.