Installing and setting up DaVinci Resolve
Go to www.blackmagicdesign.com/support/family/davinci-resolve-and-fusion then scroll down a bit, and then, on the left, you can start scrolling down until you find the version you are interested in downloading. After you find it, click on the operation system your PC is on.
If you do not already have an account, you will have to fill out a form about your information before downloading. Fill out the form and your download will start as soon as you finish.
After the download is finished. Extract the file, where inside you will find the .exe file for the program and a guide on how to install it. Follow the guide and then boot up DaVinci once you are done.
Setting up DaVinci
After launching the app, you will be presented with a short customization setup. Finish the setup according to your preferences and then you will be able to use to use the software.
Importing files
After opening the app, you will be presented to this screen. From there you can either click on "Untitled Project" which will open a new empty project, or you can click on "Import" which will allow you to select media from your PC and start with what you have selected. No worries though, you can later import more videos from your PC at any time you want.
Starting to edit
To start editing a video, you have to place it on the track, and in order to do that, you have to left click with your mouse on it from the media tab you have on the left, start holding it and then drop into the timeline below, where the video and audio tracks will separate. From there you have to edit each of them separately.
If you would like to make a cut in a specific moment of the video, you can press B which will switch to "Blade Mode", and then you can hover your mouse over the video/audio track on the frame where you want to make the cut. After that you just left click with your mouse. The cut will only apply to the track you have selected, and if you want to replicate the cut for the audio track for example, you go to the mouse on the audio track in the same place you made the cut on the video track. DaVinci will see that you're trying to make a cut in the same place so if you get really close to it, it will stop your cursor for a small time which will help you make the perfect cut. After that you just left click again.
After you're done cutting you can press A to go back in selecting mode. In selecting mode you can also grab each video part and move it later on the track, which will result in the video having spaces and moments of no video/audio in between them. By doing this you can grab a portion of the clip that's at the end and place it before another portion that was before it.
How to trim?
To go in trimming, mode you have to press "T". To trim a media piece, you have to over with your mouse on the edges. From there you can slide your mouse while holding to make the video start later or end sooner.
Titles and Transitions
Titles are pieces of text you can grab from the effects library under the "Toolbox" category. There are plenty of titles to chose from. To grab a title, click on whichever one you want, start holding and then move it above your main video. This will create a second video track where you can place any future title you need. To customize a title you can click on it and use the settings tab on the right.
Transitions are pre-made videos which have the goal of linking to different videos in a way that looks good to the eye. To use a transition, go over to the video/audio transitions tab under the toolbox section, from where you can select any transition you want and then place it between 2 videos/2 audios, You can move it around to make the transition capture more of the first or more of the second clip depending on the preferences.
Using keyframes. 
In order to use keyframes, you have to click on the video you want to add keyframes to. The settings tab will appear on the right. From there you can scroll down until you find the "Composite Tab", after you find it, switch to "Selecting" mode on the video by placing A, then move your mouse to the frame where you want the first keyframe to be. After you found it, go back to the composite tab, click on the small square button to place it, then select your type and video opacity. To place the second keyframe, move your mouse wherever you want the next one to be (note that the second keyframe must always be later than the first one) and then repeat what you did for the first one: click the square, select the type and opacity and you're done. Your keyframes should be looking like this 
How to export your video?
In order to export your video, you have to navigate to the "File" menu on the top left of the screen. After you find it, click on it and you will be met with a list of options. Click on "Quick Export" and then select which format you want to export the video in depending on your preferences. The best option is usually H.264. After you chose your preferred option, just click on export and you're done. Just wait for your video to finish exporting and your new video will be done!