Getting around the island of Gran Canaria on public transport is really easy and convenient. Seriously, trust me. I am going to try and explain a little about the guagua bus app, which I think is the best tool to use when trying to figure out the best bus to catch in Gran Canaria.
The yellow 'Guagua' buses, are only for travel within Las Palmas city. The blue 'Global' buses, are for travel outside of Las Palmas. Whether it be to somewhere as close as Tafira or somewhere as far away as Puerto Mogan. Global and Guagua are two separate companies.
Your most helpful tool by far, is the Guagua Bus app. This can easily be downloaded at the iphone/android app store. There are a couple of different apps available but this one is the best:

Although it is called the 'Guagua Bus' app, it has all the information you might need for travelling on either the Yellow or Blue buses (Guagua/Global bus companies). You will need an internet connection/data to use the app so make sure you do your research before you travel if you do not have a sim card with data.
There is also the Global website: http://www.globalsu.es/ which has all the details of the lines and timetables for the Blue buses. And for travel around Las Palmas in the Yellow buses, there is the Guagua Bus website: http://www.guaguas.com/
The thing I love most about the app, which sets it apart from the websites, is that it will show you the map of each route, including the exact location of each stop. Here, you can check that the bus actually goes where you want and how far you will have to walk from bus stops to get where you want. You can even click on the stop that you need to find out it's exact name. The app combines both Global and Guagua, making is really easy to find your way wherever you want to go on the island.

This is the opening page of the app. The search bar/points of interest button is helpful for finding the bus routes that lead to these places whereas the 'Calculate Route' button is helpful for finding the best way to get from where you are, to where you want to go. You can use the buttons on the very bottom of the page to find out the specifics of any route of any bus line.
Click 'Municipal' for the Guagua Yellow buses, or 'Global' for the Blue buses. A list of all the possible bus routes will appear. You will see both the number of the bus, and the route (which is also displayed on the front of each bus).
Click on the bus route you prefer and a list of every single stop along that route will appear from departure - destination. If you want to see where the bus stops on the return trip, simply click on the "return" button at the top of the screen:
You can click on any stop and you will find listed its exact address and the hours of departure for that bus line. Note: the hours of departure are when the bus leaves its original departure point, they are not the times that it leaves that particular stop. You can also use the 'location' button to see its exact location on the map. Just press the 'back' button whenever you need to exit a screen.

And this brings me to the MOST helpful button you will find in this entire app. It is on the right hand side of the screen, when you are looking at the list of stops for a particular route. The "Map" button.

This will show you exactly on the map where each stop is. You can zoom to your hearts content to see street names etc and the maps are quite detailed which makes them an excellent reference. When you have internet access, or data on your phone, you can find out your exact position in relation to these stops by pressing the location button on the top right hand side of the map screen.
Tip for finding your location: If you do not have internet connection, or data, you can simply switch on your GPS and open the google maps/maps with me app. After a few minutes (you need to be patient), your location will appear on the map, even without an internet connection. It's like magic (but really it just uses satelites to find your general position)! This way you can keep a track of where you are while you are on the bus.
If you are looking at the map in your Guagua Bus app, and would like to know what the name of a particular stop is, just click on it and all the information you need will pop up. I usually take a screen shot, if the name or location is a bit obscure, to show the bus driver who usually knows what you mean.

So there is a little crash course on how to use the most helpful public transport app in Las Palmas. I have seen a lot of confused tourists out there and I know it can be a bit confusing to begin with, but it is very easy once you get used to the app.
I will be writing some helpful blogs on the best ways to get to the South/Centre/airport of the island via bus, the best public transport tickets to buy and a few other helpful things about Las Palmas in general.