You don't mention the router model though.
The first is the internal flash memory.
The second and third are the ram.
Installed packages go to flash. In case you have exhausted the flash, you can uninstall packages you installed and don't need anymore. Otherwise you can use extroot and expand the overlay filesystem.
the router model is TL-WR841ND v7
i have not installed anything yet, im sending screenshots of default values.
yes, i have already seen this page, but will getting flash memory full have any cons? i mean will it affect speed or anything?
If you only have 80 kB of free flash space (in the screenshot). forget about installing anything.
Flash memory (4 MB in your router) is totally different than the runtime RAM memory (that you have 32 MB). Both of those are so low amounts that they are problematic for the current OpenWrt.
It will possibly prevent normal working of the router after the next reboot, as the settings part will get mounted read-only.
i just want to install these packages "ppp-mod-pptp, kmod-nf-nathelper-extra" to enable pptp vpn connections.
Build a custom image to fit the required packages.
Follow the links above and read the info carefully.