From the menu bar at the top of AE Select Composition > New Compisiton
Step 2: Step Two - Composition Settings
Copy over what I have to your composition settings, feel free to change some of the basic settings such as composition name, frame rate and resolution to fit your film. Click ok when finished.
Step 3: Step Three - Creating A Solid
From the menu, select Layers > Solid
Step 4: Step Four - Solid Settings
Make sure your solid settings are the same as your composition and make sure the colour code is #000000 for straight black.
Step 5: Step Five - Creating a text layer
From the menu bar, select Layer>New>Text.
Step 6: Step Six - Editing the text layer
Edit the text layer to your liking, font, color, size etc. Make the text visible compared to your background (black on white/white on black etc.) Select the drop down menu as shown below, click on proportional grid to center your text to your composition.
Step 7: Step Seven - Creating an animation
From the effects and presets menu select "CC Particle World" and drag and drop it to the Black Solid layer.
Step 8: Step Eight - Ordering the layers
Make sure the Black Solid layer is on top of the text layer so the particles will form above the text and die out over time revealing the text. You can do this by drag and dropping the layer of the text layer
Step 9: Step Nine - Configuring the Particles
Under the particle sub-menu change the particle type to your liking. Here you can change the colour settings of your particle. Under the "physics" sub-menu, change the gravity of the particle world to anything under 0.350 to appear as it is shooting out at the camera.