Sharing Mods

Platforms

For XBox:

Make sure loose assets are available (they're going to be converted and packed)
Load your plugin in the CK as the active plugin
Tell the CK to upload for XBox.
Make sure the list contains everything you want, and nothing you don't.
Export the list once you perfect it so you don't have to fill it out again later
Hit OK
Wait for the CK to convert the files and create the two archives (if necessary)
Fill out the mod information for Beth.net
Hit export to save out the data you just filled out
Click upload

For PS4:

Make sure loose assets are available (they're going to be converted and packed)
Load your plugin in the CK as the active plugin
Tell the CK to upload for PS4
Import the list you made earlier for your XBox version (you did export a list, right?)
Hit OK
Wait for the CK to convert the files and create the archives (for now, because PS4 texture conversion is not supported, no texture archive will be made - attempting to make one yourself will crash the game)
Import the beth.net information you made earlier (you did export it, right?)
Click upload.

The most common cause of crashes before the add files window opens is a bad nif file, due to the CK going through each model referenced in your mod to get a list of textures and materials.
There is no reason to add INI Fragments to your archive. The CK will automatically detect and upload a correctly-named ini as part of the package uploaded to Bethesda.net.
For multiplatform uploads you can add "[XB1]" or "[PS4]" to the end of your mod name to tell them apart (the import/export process will tack them on for you) and the game will trim off those specific suffixes if it sees them (so users on those platforms just see the normal mod name).
Once you have a ESM you want to upload to Beth.net, simply load it into the editor normally, without any plugins loaded, and select the upload option like you would for a plugin. The CK will detect no active ESP and ask you if you want to upload a masterfile instead, where it will then let you select which masterfile to upload. Proceed through the upload process as normal.