Before you deep dive into Describe calls and SOQL you might want to catch up reading about relationships in general. It's a long read and you'll probably frown that you know most of it already but it'll make your knowledge bit more systematic. You might also want to play with queries in Force Explorer, Eclipse or similar SOQL tool. That way you'll know what's the result you're after and describes will only get you there with proper column and rleationship names.
If you have a background with normal relational databases (LEFT JOIN etc) - it all depends from which side you'll start the join.
This will give you all Contacts (including those without Account):
SELECT Id, FirstName, LastName, Email, AccountId, Account.Name FROM Contact
This will give you all Accounts (including these that don't have any Contacts)
SELECT Id, Name, (SELECT Id, FirstName, LastName, Email FROM Contacts)
By applying WHERE clause you can limit the results so the end result could be similar in both cases (all depends on which side of relation you're more interested in...).
Check these for more goodies: How can i get the id of the max record?, REST API query to get all accounts which have child records?
Best Answer
If you know the object key prefix then you can view records of that object:
Let's say you have a custom object and its has key-prefix is
a00. You can view its record by going to URL:https://na9.salesforce.com/a00 (https://
sfdc_instance.salesforce.com/objectkeyprefix)Key-prefix is the first three characters of object's any record.