I recently downloaded some synths including the ample sound ABPL and AGML. But being an amateur I don't know how to set a different sound and how to upload my own recorded sounds to the synth. Please help me out. Thanks.
I think you downloaded not only guitar VST-s (ABPL, AGML).
I don't know much about those two guitar VST-s but I may be able to help you about the synts.
For most of the synths the settings, oscillators are relatively the same fortunately.
I learned most of the thing I know and use from this video and the following part:
They are old but what he's talking about and teaching is valid even nowadays. In the first video he's even talking about how sound works and how is it "build" in general.
Your own recorded sound could be used as a sample. DAW-s provide piano roll even for samples and as far as I know most of them provide basic ADSR settings and filters as well so you can play around your own sound "synth-like".