Insert an effect for one bar, not the entire track

I have a track that I want it to sound the like a few of the tracks drop off., but i do not want it effecting the rest of the track. How do I do that?

If you mean you just want to have a section fade out, you can use the Split tool to create a separate event of the section you want to fade, then grab the white triangle at the upper corner and create a fade.

If you’re trying to do something a little more involved, on Windows, you Ctrl + right click on the event or selected range and go to the plugin menu to select the plugin you want to apply, or processing menu if you want to process audio. The offline processor will come up either way along with a dialog asking if you want to apply processing only to the new copy of the audio that Cubase has created or to all copies. Make your selection and click OK to apply processing.

More here:
https://steinberg.help/cubase_pro_artist/v9/en/cubase_nuendo/topics/audio_processing_and_functions/audio_processing_and_functions_c.html

Alternately, you could cut the part you want to apply the effect to and move it to it’s own track which you can apply the plugin to. You may want to extend the event slightly in each direction and apply very short fades to make sure there is no audio glitching. You may need to do the same to the cut point in the original track. This would be the preferred way if you are applying a plugin, not processing, and wished to automate parameters of the plugin that you may want to edit easily.

You also could insert the FX and use an automation to switch it on where you want it to work and switch it off for the rest of the track.