How do I connect to UOX3 with an UO client?
For a more detailed answer to this question, check the Connecting to UOX3-page in the UOX3 Documentation, which should also exist in your local .\UOX3\docs\ folder.
The summarized version goes like this:
UOX3 is currently compatible with UO Client-versions from ~4.0.11c to 7.0.86.2 "out of the box". Encryption must be removed from the client before UOX3 will accept any connections from it, which means an 3rd party tool will be necessary for patching out this encryption either temporarily or permanently. Below follows some instructions on how to do this using one such tool, Razor.
1) Download and install Razor or a different tool that can patch out the client encryption
2) Start Razor, make sure the "Patch client encryption"-flag is enabled, then enter your UOX3 shard's IP-address and Port as defined in UOX.INI. If Razor fails to auto-detect your client installation-folder, or you have multiple ones, specify the locations of the folders yourself in the right places (one for folder, one for client.exe).
3) Press the "Okay"-button to launch the UO client, and then login using the username and password you setup in accounts.adm when you first configured UOX3
Another alternative is to use UOClassic - an open source, cross-platform UO client that doesn't require the use of Razor to connect to UOX3.