Assuming you are using Ubuntu 12.04 (Precise), you can just point and click to install FLDIGI using Ubuntu Software Center.
There are 2 methods I use, and both are easy. The methods are essentially the same, but install different versions of the FLDIGI software package. I use method #2 mostly.
The first method will install the current software package (FLDIGI) available within the current release of Ubuntu. As I type this reply to your question, that would be Ubuntu version 12.04 (Precise), and the current FLDIGI package available for installation is FLDIGI (3.21.38-1).
#1 Click on "Ubuntu Software Center"
#2 Search with Ubuntu Software Center for the application "fldigi" ( the box - upper with magnifier glass symbol ).
#3 When the search results are displayed that show the package/application "fldigi" - click install - be patient - the installation is slow - about 1 to 2 minutes, and there is some, but not a lot of feedback from Ubuntu about the installation process. Ubuntu has to install the package (fldigi) and it's required dependences.
#4 Setup - Configure the fldigi application to meet your digital mode hardware requirements.
This is a very easy method to install the latest and greatest version release of FLDIGI. Again... as I type this reply to you, that would be version fldigi (3.21.48-1). It seems that the developers of fldigi fix bugs brought to their attention in a VERY timing manner. FLDIGI is a very well maintained Linux amateur radio application. The work is done by a core group of Linux software developer hams working together to support the amateur radio community.
#1 Google search "Ubuntu packages" - the search results will reveal a link to www.packages.Ubuntu.com
- click on that link. You will see a page "browse through the list of packages". Find the package set under "quantal" ( this is Ubuntu version 12.10 it is not released yet ).
Find the package group "HAM RADIO".
Find fldigi (3.21.48-1 [universe] - click on that link.
Scroll to the bottom of the page... "Download fldigi"
Click on the architecture you use amd64 (64bit) or i386 (32bit). This will be up the actual download page (mirrors). Click a a mirror link and select "SAVE" the file. I use "North America" and "ubunut.media.mit.edu" sometimes i use "rit.edu" also.
This will download the fldigi file to your HOME directory DOWNLOADS folder. When the download is complete - close your web browser, and open the file manager Nautilus, and locate the file you just downloaded in the Home directory Downloads folder... the file should be either : fldigi_3.21.48-1_amd64.deb or fldigi_3.21.48-1_i386.deb again, it depends on the computer architecture you are using.
Now to install FLDIGI - Right Click and select "Open with Ubuntu Software Center". Like I stated before there is not a whole lot of feedback during the install process ... SO BE PATIENT! It will install!
#2 Setup - Configure the fldigi application to meet your digital mode hardware requirements. Enjoy.
It seems like a lot, but this method take 15 to 20 seconds to implement.
This method should be able to be used for future Ubuntu and Fldigi releases.
It works well for me.
With a old spare computer,and a free high tech operating system like Linux, and a free digital mode software application like fldigi, I spend my money on other ham gear. Thank you fldigi developers very much.
I hope this helps you. N1ISA