How should i edit the file /etc/security/limits.conf by editing core or cpu field value

<item> can be one of the following:
# - core - limits the core file size (KB)
# - data - max data size (KB)
# - fsize - maximum filesize (KB)
# - memlock - max locked-in-memory address space (KB)
# - nofile - max number of open files
# - rss - max resident set size (KB)
# - stack - max stack size (KB)
# - cpu - max CPU time (MIN)
# - nproc - max number of processes
# - as - address space limit (KB)
# - maxlogins - max number of logins for this user
# - maxsyslogins - max number of logins on the system
# - priority - the priority to run user process with
# - locks - max number of file locks the user can hold
# - sigpending - max number of pending signals
# - msgqueue - max memory used by POSIX message queues (bytes)
# - nice - max nice priority allowed to raise to values: [-20, 19]
# - rtprio - max realtime priority

I need to limit the cpu cores to 10, limit memory(RAM)10GB and Home folder quota for user directory 10GB

Hello and welcome to LQ. Hope you like it here.

Assigning cores and setting quota isn't a task for pam_limits.so and as for your other question please read 'man 5 limits.conf' and propose what you should configure. That way we at least have an idea you know what you're talking about because with all due respect this looks much like homework to me.