Remote Computer:foobar.com
Current Directory: /home/chr1x2
Remote Directory: /home/foobar/backup
Local File: file.txt
Remote File: elif.txt

Go to the your local directory where you want to download or upload the file:

$ cd /home/chr1x2

Connect to remote host. Enter username and password when prompted:

$ ftp foobar.com

Use binary mode when transfering files:

ftp> binary

Uploading:

Go to the right directory of remote host where the file.txt should be uploaded:

ftp> cd /home/foobar/backup
250 Directory successfully changed.
ftp> put file.txt
ftp> ls
file.txt
226 Directory send OK.
259 bytes received in 0.00043 seconds (586.44 Kbytes/s)

Downloading:

Go to the right directory of remote host where the elif.txt can be downloaded:

ftp> cd /home/foobar/backup
ftp> get elif.txt

Exit ftp and check the file you downloaded:

ftp> bye
$ ls
elif.txt