yes things like envelopes and lfos are not just in flstudio indeed (its not called fruity loops anymore).
An envelope is something that you can use to control some parameter over time in a certain way. command paramters for an envelope is : attack, decay, sustain, release.
Attack is how long it takes for the sound to fade in, decay how long it takes to fade out, sustain is the level the sound continues playing in at the end fo the decay. the release lets you fade the sound out after the gate signal stops. (this is where the note end in the piano roll, think of it like htis, when you push a key on your midi keyboard its a gate on, when you release the key its a gate off). You have 5 individual adjusatable envelopes in the sampler machine, for 5 differnet params (internally in the sampler), i suggest you use them (just start simple and use the Vol one only)
LFO, Low Frequency Oscilator. Again, this is a tool that can be used to control a paramter over time. except in the case of the lfo its continues, instead of just a one shot fadein, sustain, fade out. This one changes a parameter over time following a oscilator . sine and triangle just go up and down between a range really smooth like, you can use a square osc to constantly switchy between 2 values, noise lfo to constantly have a random value, etc. expirement and mess around
. To control a paramter in flstudio with an lfo (and this can be ANY paramter anywhere, (even the BPM), and also goes for a lot of other different machines (peak controller, etc)), right click the control you want to modulate with an lfo and select 'linkt to controller....' . somewhere in the middle of the dialog is a section where you can assign an 'internal controller', select your lfo or peak controller or whatever output in there.
This is very powerful stuff and enables you to create so many new interesting sounds and soundscapes. Its well worth learning.
And just a random tip, for your drums: instead of having a piano roll pattern for your kick, and a piano roll pattern for your snare, and a piano roll pattern for your hihat, etc, there are two ways of going about that more efficiently.
1. forget the piano rolls for your drums, and just use the step sequencer for your drum hits, for drums its a lot faster and you dont always need to change pitches and such. if theres something you want to do to something later that can only be done in the piano roll, just right click the machine in the step sequencer and select 'send to piano roll...'
2. Add a layer machine. If you use a layer machine you can assign all your drum sampler machines to be controlled by the one layer, and this way you can put all of your hits again in one pattern (if you want). Now ive already explained a few things, and i like to leave some thigns open for people to go discover themselves. so if you want to follow this step you need to read the help manual, in particular the section on the sampler machine , and the section on the layer machine.
I hope this helps you at all. Enjoy yourself and have fun tweakin around
Peace