bitcoind in the system's $PATH variable

[crystal-love]

Trying to install lnd but it says:

"This command requires bitcoind (almost any version should do) to be available in the system's $PATH variable. Otherwise some of the tests will fail."

Was trying to find examples on the web, but could not.
How do i do this variable? 

TY

[crystal-love]

TY,
Another question, which location should i use?


$ locate -i bitcoind
/home/user/downloads/bitcoin-0.20.1/bin/bitcoind
/home/user/downloads/bitcoin-0.20.1/share/man/man1/bitcoind.1
/usr/local/bin/bitcoind


p.s. yes, its Ubuntu server.