There are a number of ways to select multiple topics. The first is to use the SHIFT button in the top left corner of the screen. The SHIFT button acts a little like a combination of the SHIFT, ALT and CMD keys on a Mac keyboard.
If you press and hold SHIFT whilst dragging your finger over the canvas, it will create a 'selection rectangle' as can be seen below.
To select (or deselect) individual topics, press the SHIFT button whilst tapping on the topic as below:
Once multiple topics are selected, you can then apply attributes to those topics (such as colour, shape etc.) You can also drag them and re-home them under another topic. If you press and hold the SHIFT button whilst dragging the topics it will duplicate them - as can be seen in the following 2 screenshots.
Whilst SHIFT is good for fine grained control of the selection, a faster way is often to simply tap the topic then choose 'Select' from the popup menu.
The Select option will then present up to 4 more options:
The Cousins option will select all topics at the same level (on all branches) as the topic tapped.
NB: If you are using an external keyboard then you can also use the arrow keys and shift key on the keyboard to select adjacent topics.
NB2: For users of the original app, this multi select approach replaces the previous 'Apply to Children/Siblings' buttons.
NB3: For those of a left handed disposition, you can switch sides for the SHIFT button in the System Settings.