You know or should know that an acid, #HX#, is a proton donor in some solvent, typically water.....and we could represent its characteristic reaction in the following way....
#underbrace(HX(aq))_"parent acid" + H_2O(aq) rarr underbrace(X^(-))_"conjugate base" + underbrace(H_3O^+)_"hydronium ion"#
The hydronium ion is a conceptual species; it is a cluster of water molecules, 3 or 4 or more to give say #H_7O_3^+#, with an EXTRA #H^+#..we write #H^+# or #H_3O^+# as a shorthand....
#H_3O^+# is the so-called #"CONJUGATE ACID"# of water, i.e. the original acid PLUS a proton...of course we conserve mass and charge. And #HO^-# is the so-called #"CONJUGATE BASE"# of water, i.e. the original acid MINUS a proton.
And using this formalism, all strong acids react in solution to give their #"CONJUGATE BASES"#. What are the conjugate bases of #HClO_4#, #H_2SO_4#, #HNO_3#?
To go to another example...what is the conjugate acid of #NH_3#. I make it #NH_4^+# (and I hope you do too). But what is the conjugate base of ammonia? This is so strong a base that it does not occur in water, but DOES occur in liquid ammonia.
Confused yet? But all I have done is to add or subtract protons, #H^+#, and CONSERVED CHARGE and MASS.....
See here and links for further examples.
