1) Basics 2) Nitty-gritty 
[general relativity] In physics, in the theory of general relativity, spacetimes with at least a 1-parameter group of isometries can be classified according to the fixed point-sets of the action. Isolated fixed points are called nuts. The other possibility is that the fixed point set is a metric 2-sphere, called bolt. The number of nuts and...
[n] - detailed practical information about how something works or how something can be accomplished
A mix of a mild and bitter ale that is popular in England (most popular in the East Anglia region).
noun detailed practical information about how something works or how something can be accomplished
the essential or basic aspects: to learn the nuts and bolts of a new job.