Yes, but only the installing is for me not clear, (where, how…)
This section is for me like suaheli 
Configuration
We have a typical client «» server configuration.
Server configuration
Use the file /etc/exports to configure your shares. Example:
/mnt/sda2 192.168.1.2,192.168.1.3,192.168.1.4(ro,sync,no_subtree_check)
/mnt/sda3 192.168.1.2(rw,sync,no_subtree_check)
/mnt/sda4 192.168.1.0/255.255.255.0(rw,sync,no_subtree_check)
You can’t use the CIDR notation, so /mnt/sda4 192.168.1.0/24(rw,sync,no_subtree_check) would not work, however the above example does.
If you set up pivot-root or pivot-overlay, use the path on /overlay/ partition, else you cannot export mounted fs.
Assuming the daemons are already running, use the command exportfs -ar to reload and apply changes on the fly.
Start on boot
Since opkg-installed init.d scripts are not enabled nor started by default, you need to do this manually. Same procedure as with most (all?) OpenWrt packages: The first commands will will start them right now, the third and fourth will create the symlinks /etc/rc.d/S??portmap and /etc/rc.d/S??nfsd so they get started on boot:
root@OpenWrt:~# /etc/init.d/portmap start
root@OpenWrt:~# /etc/init.d/nfsd start
root@OpenWrt:~# /etc/init.d/portmap enable
root@OpenWrt:~# /etc/init.d/nfsd enable
After start (and after a reboot) verify with top or ps whether the services are running.
The following entries should appear in the process list:
_/usr/sbin/rpc.mountd -p 32780 _
/usr/sbin/rpc.statd -p 32778 -o 32779
/usr/sbin/portmap
Use the netstat -l command to see whether portmap is listening on port 111 for both tcp and udp. The nfsd process may use varying ports.
Client configuration is not the problem