There are two ways to create/modify titles in Motion and use them in FCPX. First way is two right click an existing title in FCP and select send to Motion from the drop down menu that appears. Second way is to open a title template in the Motion project browser that appears when you open Motion. You then create or modify depending on whether you are working with a new title or an existing title from FCP. If you are modifying a title then just save it when you're done and it will appear in the FCP title browser. If it's a new title then publish it and it will appear in the FCP title browser. Motion is not a 3D modelling app, but you can simulate 3D effects by positioning objects in 3D space and also rotating objects around the X and Y axis and positioning them along the Z axis. Actually looks pretty good, but not true 3D modelling. Have fun!
If by "Final Cut Title" you mean the Basic Title (that you also get by typing Control-T), you can edit that title by right clicking on the Basic Title template in the Effects Browser >Titles > Bumper/Opener section, and selecting Open a Copy in Motion.
In Motion 5, turn down the disclosure triangle on Main and select the Title layer (in the layers column). Under the canvas at the bottom right are several icons -- click on the one to the right of the gear (Filters) > Stylize > Extrude. In the Inspector, select the Filters tab and right click on each one of those parameters and select Publish (that includes the Gradient). At the bottom, select the Publish OSC control (so that it is Checked.) Everything you just published will appear in the Title Inspector in FCPX.
Save As and give it a new name (although there will already be a "Copy of Basic Title" in FCPX -- happens as soon as you open in Motion) -- something like Extruded Title.
Back in FCPX, you can add that title to your storyline and use the OnScreen Control to create your 3D effect however you like it.
If you like, you can pre-setup the text to appear like you would generally like to have it in it's "starting" condition (for instance, ramp up the text size, set colors, etc.) Every time you save, however you have the title set up in Motion is how it will appear in FCPX when you add it.