LM 2577 is boosting up voltage, but will it boost up current too? What is the meaning of max 3 Ampere current output? If I have input 5V, 100mA, will it boost up the current e.g 12V, ?? A.
No.
This is not a perpetum mobile
In all case:
if you need more output current you must have lower output voltage_ only than is your sum of energie the same(minus effivciency of converting)...
In only one situation can you have more output current (more energie) as over that I wrote: if your current consum is for short time!! In tihs case you need storidge elements, capacitors, & pulsed load!!
K.
Added after 3 minutes:
Current boosting:
Clear, output current can be high as max 3A (w. LM2577 & proper dimensioning), what I wishd to wrote: wil be never more enerige go out as in (& 70-80%(in)efficiency)....