The following excerpts from the Tor Project Manual should tell you everything you need to know:
ExitNodes node,node,…
A list of identity fingerprints, nicknames, country codes and address patterns of nodes to use as exit node---that is, a node that
delivers traffic for you outside the Tor network.
Note that if you list too few nodes here, or if you exclude too many exit nodes with ExcludeExitNodes, you can degrade functionality.
For example, if none of the exits you list allows traffic on port 80
or 443, you won’t be able to browse the web.
Note also that not every circuit is used to deliver traffic outside of the Tor network. It is normal to see non-exit circuits
(such as those used to connect to hidden services, those that do
directory fetches, those used for relay reachability self-tests, and
so on) that end at a non-exit node. To keep a node from being used
entirely, see ExcludeNodes and StrictNodes.
The ExcludeNodes option overrides this option: any node listed in both ExitNodes and ExcludeNodes is treated as excluded.
The .exit address notation, if enabled via AllowDotExit, overrides this option.
To use a country code in the ExitNodes
line you specify its ISO country code in brackets. Eg. ExitNodes {us}
to use exit nodes in the United States.
StrictNodes 0|1
If StrictNodes is set to 1, Tor will treat the ExcludeNodes option as a requirement to follow for all the circuits you generate, even if
doing so will break functionality for you. If StrictNodes is set to 0,
Tor will still try to avoid nodes in the ExcludeNodes list, but it
will err on the side of avoiding unexpected errors. Specifically,
StrictNodes 0 tells Tor that it is okay to use an excluded node when
it is necessary to perform relay reachability self-tests, connect to a
hidden service, provide a hidden service to a client, fulfill a .exit
request, upload directory information, or download directory
information. (Default: 0)