How do I know what the effect I have used is called?

Effects and presets are different things. Presets can contain effects, but don't have to. 
Both can be chosen from the Effects and Presets panel - presets are at the top, under a top-level folder named "Animation Presets."

If you're just trying to apply an effect that's already present on one of your layers, choose the layer with the effect and do one of the following:
- Twirl the layer open, and look under Effects.
- Press E to reveal effects.
- Select the layer, then look in the Effect Controls panel.
You can then copy/paste this effect from this layer to any other(s).

Once you apply a preset, there's really no way to see the name of that preset any more, because it can be made of up multiple effects, properties, keyframes, etc. on a single layer. You can use the techniques above to copy/paste the applied results of that preset from one layer to another, or:
If you go to your top menu bar -> Animation -> Recent Animation Presets, you'll be able to see what you've used recently. Unless you've used a ton of other presets, it'll still be in this list.