With iPad is possible, but not free. For decent guitar input you need an audio interface with instrument level input, and if your iPad doesn't have USB-C and the interface doesn't come with Lightning cable, you need the misleadingly named "lightning camera adapter" that is actually a generic Lightning to USB2 adapter.
You also need an amp modeling app, which may be bundled with the interface or bought separately. The free versions that come bundled with audio interfaces are typically limited to few amp models and effects and charge extra for larger selection. On the other hand, because iPad has a lot more processing power than the tiny processors in multi effects and entry level modeling amps, the modeling can be better.
Finally, you need wired speakers or headphones. Bluetooth, AirPlay and others have too much latency to be useful and the built in speaker doesn't really cut it. iOS itself has well designed audio system and can have latency around 10 milliseconds, similar to standing three meters away from the speaker.
That being said, I have iPad, iRig HD, AmpliTube and BiasFX and in my opinion it can sound convincing and playing with effects can be fun for a while, but I have found that a small practice amp is more fun to play.