There are multiple ways to customize Windows 10's start menu to your needs. Here's how.
1. Change tile size
Open the start menu (1) and right-click the affected tile (2). Then, click "Resize" (3) and select one of the options (4). Note that, while all tiles support "Small" and "Medium", not all of them support "Large".
In this example, I've switched from "Medium" to "Small".
2. Move tiles
To move a tile, left-click and drag the tile to its new location. Existing tiles will shift automatically to make way for the new tile. Release the mouse button to make the change permanent.
3. Group tiles
Groups help better organize your start menu. Simply drag an existing tile onto another to create a group. Drag additional tiles onto the group to add them to the group. To remove tiles from a group, simply drag and drop them outside the group.
4. Launch programs from a group
Groups have to be expanded before their applications can be launched. Left-click a group to expand it (1).
Contained icons will then be displayed as individual tiles. Left-click to launch the desired application (2).
Click to arrow the collapse the group when you're done (3).
5. Rename group
Names help tell groups apart. Drag the affected group slightly downward to increase the distance to surrounding tiles (1).
This will reveal the title bar, once you point at the group (2).
Click the textfield to enter a name for the group. In this example, I'll use "Ashampoo Office 2018" as title (3).
6. Unpin tiles
If you need more space, you can unpin existing tiles from the start menu. Simply right-click a tile (1) and select "Unpin from Start" (2).
7. Resize start menu
You can resize the start menu like any program window by dragging the top / right edges (1). The tiles will automatically rearrange to make the best use of the available space.
8. Add program tiles
To add tiles, drag the affected icon from the list (1) into the tiles area (2). Alternatively, you can also right-click the list entry and select "Pin to Start".
9. Additional start menu settings
Additional start menu settings are available through the Windows settings dialog. First, open the start menu (1) and click the cog wheel icon (2).
Then, select "Personalization" (1).
Next, select "Start" (1). There are various settings available. For example, you can show / hide recently used applications (2) or display the start menu in fullscreen mode (3). Simply close the dialog, when you're done.
A quicker way to access start menu settings is by right-clicking the taskbar and selecting "Settings".