Dimension table in data warehouse generally contains textual attributes which can be used analyze the data stored in fact table.
e.g. Customer Dimension Table
Above customer dimension table contain customer attributes like name, birthdates, City, Country which can be used to analyse the data like,
e.g. Top Customer Location by Revenue
Dimension also contain hierarchies which are very useful to perform drill-down, drill-up operation using BI tool.
Generally each dimension table has one surrogate key which is non-meaningful numeric created for the sole purpose of identifying dimension record uniquely. Using surrogate key as primary key of dimension table is the best practice of data warehouse and you should avoid using Business key as primary key of dimension table.