to put them is one question. You can put them anywhere as long as the location is included in your $PATH, to see the current value of $PATH just use this:
There are other factors that can prevent the scripts from running, for example, if the partition that holds that location is mounted with the "noexec" mount option. Also note that other options ("user" rings a bell) imply "noexec". By default, on most distros, /usr/local/bin is in the system $PATH, but that's not necessarily true in all distributions.
to modify your $PATH to include any arbitrary location is an entirely different question, and that depends on the shell you use. Most of them will read /etc/profile, per-user settings are defined in each shell init files, for bash that can be ~/.bash_login, ~/.bashrc or ~/.bash_profile depending on what do you exactly want to do. Other shells will use different config files, so, check your $SHELL man/info page or documentation.