I always try to come up with the simplest solution. A couple easy ones come to mind.
1 - The sp_help command gives you a wealth information. The first call below executes it for one table, and the second call below executes it for all tables.
-- Use corect database
USE AdventureWorks2012
GO
-- One table
sp_help 'person.person'
GO
-- All tables
DECLARE @STMT VARCHAR(128) = 'EXEC SP_HELP ' + char(39) + '?' + CHAR(39);
EXEC SP_MSFOREACHTABLE @STMT
GO
2 - While this gives you textual information on data types and relationships, it does not supply it in graphical form.
SSMS has a diagram feature that will show the relationships between the tables. I created a diagram for a couple of the tables in the person schema and one in the sales schema.
The downside of this utility is that the data types are not shown in the picture. However, opening the properties pages will allow you to drill into a field (column) and find all the about it.
3 - Last but not least, you can always purchase a third party tool that does it better.
I have a several blog talks using the AUTOS toy database. The diagram below was created from Oracle's ERD package. The nice advantage of this tool is that both the data types and relationships are shown in the picture.
In short, it fixes the short comings of the SSMS diagram tool. Also, given a DDL script from DB2, ORACLE or SQL Server, it will generate a diagram.
In short, picture a solution that fits your budget and you are comfortable with.