Staging instead of launching

[KhanFoil]

I am building my first liquid fuel rocket. I have used two stages with the first stage consisting of two fuel tanks and the LV-T45  liquid fuel rocket. I put a decoupler under the capsule and above the fuel tanks that start the bottom stage.

When I put the rocket on the launch pad, I hit X (PS4) to launch it and I hear an explosion, but nothing happens. I do it again, explosion, nothing happens. When I look at the flight log it lists stage separations.

What am I doing wrong?

[Vanamonde]

Sounds like you put the parts in the right order, but not the staging. Can we see a screencap of your craft with the UI included? 

[Fraktal]

Have you throttled up (gauge on the left side of the navball)? Even if you activate the engines, they won't fire if your throttle is zero. SRBs didn't need throttle, hence why you're only running into this problem now.

Edited December 25, 2019 by Fraktal

[Superfluous J]

Remember, there's no "launching" in KSP per se, it's just the stage that happens when you stage for the first time.

As was said above, though, most likely you're not throttled up or don't have things in the correct order.