Where/which is best solution for following FAQs on apt installation:

Question

I observed that Following main Questions which are frequently asked usually tagged with apt or software-installation with command-line or dependency:

• Unable to locate package:

  E: Unable to locate package [pkg]
  

• Package has no installation candidate:

  E: Package '[pkg]' has no installation candidate
  

• Packages have unmet dependencies:

  The following packages have unmet dependencies:
  package1 : Depends: package2 (>= x.y) but [pkg] is to be installed
  E: Unable to correct problems, you have held broken packages.
  

Where [pkg] means package-name.

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From which we have already Questions as follows:

• For Unmet dependencies: How do I resolve unmet dependencies after adding a PPA?
• For Unable to locate package I've prepared (which needs to improve): Unable to locate package

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For new users of Ubuntu and command-line, further method of installing software properly,

It needs to prepare FAQ type wiki/solution on above (3) Main/Considerable Q/A.

(In other words) We should have locked and best single (or max 3 linked) Q/A on above topics. which could be best contributive effort to have knowledge-based solution/information.

Answer 1

Right now, all topics you mentioned already have canonical solutions:

E: Unable to locate package [pkg]

Can have multiple reasons:

1. You don't have the repository that provide the package.
2. You haven't updated your package repositories.
3. You have misspelled the package name

There are two question that addressed this issues:

• "Unable to locate package" while trying to install packages with APT
• "E: Unable to locate package update" when I try to update my system, why? (a special case where people try to update their packages)

All those questions are apt issues. Nothing to do with the command line, software installation or dependencies. It can happen with any package manager, but ultimately apt is the one trowing errors.

E: Package '[pkg]' has no installation candidate

This already has a canonical question What does Package <package> has no installation candidate mean?

The following packages have unmet dependencies:
package1 : Depends: package2 (>= x.y) but [pkg] is to be installed
E: Unable to correct problems, you have held broken packages.

I don't know how many times I have to reference this answer, those issues are unique to the package that trows the dependency error, hence there are thousands possible solutions/answers depending the packages involved, so doing a single question don't actually help. In fact most questions about these issues should be closed as "unclear what you are asking" with a comment referencing this question in hopes the information is provided:

To help you we need you to include the information as solicited on [this
other question](https://unix.stackexchange.com/q/121180/41104). Edit your
question and add all the relevant information.

So, is quixotic to try to do a canonical question out of this issue, in theory it seems "fine" but in the practice is just a mess. That's The Right Way™.