There are several  programs that extract the documentation in the database(if there are some).
To get a simple list over the documentation of tables and columns:

select object_schema_name(ep.major_id) [Schema],
        object_name(ep.major_id) TableName,
        c.column_id ColumnId,
        c.name ColumnName,
        ep.value [Description]
    from sys.extended_properties as ep
    inner join sys.sysobjects as so on so.id = ep.major_id
    left outer join sys.columns as c on c.object_id = ep.major_id and c.column_id = ep.minor_id
    where so."type" = 'U' and so.name <> 'sysdiagrams' and ep.class_desc = 'object_or_column' and ep.name = 'MS_Description'
    order by object_schema_name(ep.major_id), object_name(ep.major_id);