First digit in the above mode number is used to set setuid, setgid, or sticky bit. Each remain digit set permission for the owner, group, and world as follows:
4 = r (Read)
2 = w (Write)
1 = x (eXecute)
So you end up creating the triplets for your user by adding above digits. For e.g.
To represent rwx triplet use 4+2+1=7
To represent rw- triplet use 4+2+0=6
To represent r– triplet use 4+0+0=4
To represent r-x triplet use 4+0+1=5
To only give full permission to user, use it as follows:
chmod 0700 file.txt
0 – Use set setuid, setgid, or sticky bit
7 – Full permission for owner (rwx = 4+2+1=7)
0 – Remove group permission (— = 0+0+0=0)