apt-cache

To search for available packages, run

apt-cache search PKG_NAME

Example

boby@sok-01:~$ apt-cache search wget
devscripts - scripts to make the life of a Debian Package maintainer easier
wget - retrieves files from the web
abcde - A Better CD Encoder
apt-mirror - APT sources mirroring tool
axel - light command line download accelerator
filetea - Web-based file sharing system
getdata - management of external databases
libcupt4-2-downloadmethod-wget - flexible package manager -- wget download method
libwget0 - Download library for files and recursive websites
ow-shell - shell utilities to talk to an 1-Wire owserver
puf - Parallel URL fetcher
pwget - downloader utility which resembles wget (implemented in Perl)
python-wget - pure Python download utility for Python 2
python3-wget - pure Python download utility for Python 3
snarf - command-line URL grabber
tcllib - Standard Tcl Library
texlive-latex-extra - TeX Live: LaTeX additional packages
wget2 - file and recursive website downloader
wget2-dev - development file for libwget2
wput - tiny wget-like ftp-client for uploading files
boby@sok-01:~$ 

Ubuntu find Dependencies for a package
apt