Place these machines directly adjacent to one another, in this order:
[mass fab][replicator][pattern storage][scanner]
The scanner must be next to the storage so it can save the patterns it scans. The replicator must be next to the storage so it can use the patterns to replicate something. The mass fab is next to the replicator so you can use a liquid ejector upgrade to shunt the uu-matter it produces into the replicator. Yes, uu-matter is now a liquid.
Obviously there are other solutions - crystal memory disks allow you to carry patterns between machines that are not physically touching, and other mods that add liquid piping solutions and tanks can store and transport uu-matter like any other Forge liquid. But the above is the most basic setup.
Scanner and mass fab take up to 512 EU/t. The scanner will take a bit less than that to scan, and nothing to sit idle; the mass fab will take everything it can get, and will accept transformer upgrades to get up to 8192 EU/t. The pattern storage does not need nor accept power. The replicator can take up to 2048 EU/t but uses well less than that. However it can accept overclocker upgrades to increase its working speed, and also another transformer upgrade to 8k if necessary.
Currently uu-matter is not fully implemented and there are only a handful of items scannable. I know of around 18-20 possible recipes. Generally, if it's from vanilla or IC2, and can be found by digging or mining, it can be scanned. Exceptions may apply (I'm a few builds behind).