1
Open your Start Menu.
Click the button to show the long alphabetical list of installed apps on your Start Menu.
In that list, you will find the Office Apps (Word, Excel...etc.).
Right click each app[, and you can select 'Pin to Taskbar' to put the apps on your Taskbar.
Or you can drag an Office app from that long alphabetical list onto your Desktop to create a new Desktop icon for the app.
2
For the other problem.
Right click a Word file and select Properties.
On the resulting Properties dialog, click the Change button.
In the resulting list, select Word to open the file.
That will set the file associations for Word documents.
You can perform the same process for Excel, PowerPoint... etc. and other Office files.