After installing the package, how can I track back?
 

I just install a package by typing:
installpkg somepackage.tgz

after that is done, I don't know what command to launch the application, I did try the software name, but it doesn't work. So how can I track back to find out the launch command?

Thanks

You can try typing in man somepackage for the manual page to see if that helps. You can see if you can find a file with locate or find / | grep file_name. Is there a specific program or is just in general terms?

It would have been logged in /var/log/packages/packagename. Look for where it installed the binary and run that. Probably xxx/bin/ or xxx/sbin/.

When I look at /var/log/scintilla158
It has this information, but I don't know where the intilla directory is. I try to find it in /usr, /usr/local, but just can't find it.

Hmm, that looks like source tarball (ie src in the filename, probably) vs a pre-compiled binary package. If so, you'll have to compile & install it yourself, or find a binary package for it. As far as where it's located, l'm not sure. Use locate as suggested above, or "locate intilla" to find it. But's probably wherrever you unpacked it, or wherever Slackware places it's source packages by default. I'm not sure about the later, as I always download and use a vanilla source vs Slackware's source packages.