Well is I understand the situation (but I could be wrong)
Block Mixing Is done in the ingame editor using
TMulimiter. Mostly to play these tracks you do not need to use or have TMunlimiter. But there are a few exceptions like when blocks are outside the play area you can only play the maps using TMunlimiter. TMunlimiter only works with the specific game version/update it was made for, so for each new version of the gamed a new version of TMunlimiter has to be made.
Custom blocks are actually known as
Custom Objects. You must have the objects installed locally to be able to use them in the editor. To use them on a server can only be done by playing a Title that includes custom objects. The best place to keep an eye on new object is on maniapark. The best place to learn how to make them is on the maniaplanet forum. You will need other tools such as a program capable of producing 3ds files to be able to make your own objects.
Custom Scripts are actually a game mode, like TimeAttack or Rounds are. There hasnt been alot of this done in TM2 yet, But alot have been made for SM. Scripts can be written by anyone if you know how and have the coding skills. You do not need anything installed to play on a server running a custom script. Maniapark is the central storage for available scripts
Titles are a package that could possible include many different things, objects, game script, maps and more to give specifc Play. You must have a title installed to be able to join a server playing a Title. Titles are added into an empty station slot on the maniaplanet main menu.
The best place for tutorials is possibly mania-creative but you will find valuable info on mania-planet forum.
At this stage mania-exchange is keeping to its core of being a map depository and tagging requirements if they exist, but not being a download place for them.
If within our members here we have the motivated and skilled people it is possible MX could create our own Title.