Intallation Widgets on homescreen

When I push the homescreen for a few seconds the configurationscreen pops up. I want to install a widget on my homescreen that predicts the weather and shows the time. When I select 'widgets' (the middle one on the screen) a few items are showed but NOT the apps I have downloaded. Somehow they are just not visible and therefor I cannot select them and put them om my screen. Very frustrating. I have downloaded at least 5 different weather-apps, none of them turned up in the list of available widgets. Whatsapp is visible in that list, as well as Settings.  I hope you can help!