It takes a little practice, but, basically you will draw a path and then keyframe how it uncovers itself over time. One way to start is to hand-draw what you want on paper first, and scan it in as an image file. Then you can bring that into Motion as a background layer, and trace over the lines with your mouse or pen cursor, in the vector line drawing mode. Then delete or make the guide layer invisible. Doing stuff with particles will be very similar, the particles will emit from whatever path you draw. As you get more sophisticated you might bring in vector files made in other applications and apply parameters to those as well. Start slowly, just draw and animate one large letter, and play around with the settings.
Here, let’s animate a crude letter W. Create a new project in Motion, grab the bezier pen tool and sketch out the letter W.
Now, go to the inspector pane, turn off “fill color”, we only want an outline color. The next part is the secret sauce they wouldn’t tell you for free, but I will: See the controls for “first point offset” and “last point offset”? To get the “w” to write itself onto the screen, you just pull down the last point offset to zero, set a keyframe, go a second or so down the timeline, and advance the last point offset to whatever the end limit is, and as you drag that control you can already see the line “writing” itself. Play that back; it should draw out the line for you. Now go back and play with the other attributes in that control box for the thickness of the line, and what the ends look like. If you understood all this so far, you know everything those people charging you money wanted you to pay for, the rest is just practice and experimentation.
Did that help?