Plugins are brilliant, well they are when they work and when they all work together nicely. Because plugins are written by different people there can be times when a plugin doesn’t do what it says on the tin and can make your site look odd. Don’t activate a whole bunch of plugins at once. Take it easy and do one at a time in case there is a rouge plugin in your downloads.
How To – I would always recommend going through your WordPress dashboard for plugins and not just grabbing new ones off the internet. In your WordPress dashboard go to the plugins section on the left and then to ‘add new’ . in the search box type in the name and press search. The search box is very finicky so if you know the name of the plugin make sure you have spaces and capitals all in the right place.
Once you found the plugin you are after and happy with what it does, click install and then activate. Then check your site is behaving properly before you go onto the next plugin you want.
Oh and if you decide a plugin isn’t for you, you can easily deactivate it but always delete off the ones you don’t use.