Memcheck is Valgrind's default tool; you do not need to pass it explicitly, but can do so with the valgrind --tool=memcheck <program-to-execute with params> syntax.
As a trivial example, let's run Valgrind on the df(1) utility (on an Ubuntu box):
$ lsb_release -aNo LSB modules are available.Distributor ID: UbuntuDescription: Ubuntu 17.10Release: 17.10Codename: artful$ df --version |head -n1df (GNU coreutils) 8.26$ valgrind df==1577== Memcheck, a memory error detector==1577== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.==1577== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info==1577== Command: df==1577== Filesystem 1K-blocks Used Available Use% Mounted onudev 479724 0 479724 ...
