In the following examples, I'm using [c-] for holding down control while hitting other keys. [c-a,B] means hold down control and hit lower case a and then upper case B. I.e. press control, press and release the 'A' key, press shift, press and release the 'B' key, release control.

Window (viewport) management.

Make first (topleft window current):
  c-w t

Change current window to full-width
in top position:
  c-w K

Change current window to full-height
in left-most position:
  c-w H

To change terminal with a single vertical split
to a single horizontal split:
  c-w t c-w K

To go horizontal split to vertical:
  c-w t c-w H

Resizing viewports.
  3 ctrl-w +    increase height by 3
  3 ctrl-w -    decrease height by 3
  3 ctrl-w >    increase width by 3
  3 ctrl-w <    decrease width by 3
  ctrl-w =      equalize width and height, all windows

vim digraphs in insert mode.

A long list of vim digraphs

Hit [c-k] and then the two characters forming the digraph.
You may need to hold down shift for some.
  [c-k]+-    ±
       DG    °      degree
       <<    «
       >>    »
       e'    é
       e`    è
       12    ½
       oe    œ
       o^    ô
       c,    ç
       a*    α      *a also works
       m*    μ
       p*    π
       w*    ω
       W*    Ω
       2S    ²      superscript
       2s    ₂      subscript
       +S    ⁺
       ->   →
       hh    ─
       HH    ━
       vv    │
       dr    ┌
       PR    ▶
       Tr    ▷
       0u    ☺
       Md    ♩
       M8    ♪
       M2    ♫
Some digraph combinations:
  dr dl    ┌┐
  ur ul    └┘

vim unicode while in insert mode.

Characters using [c-v] followed by three decimal digits.
Only 000 to 255?
  [c-v]177     ±

Characters using [c-v]x followed by two hex digits.
x00 to xff.
  [c-v]xab     «
        b1     ±
        b2     ²

Characters using [c-v]u and then 4 hex digits.
for the unicode.
00000000 to ffffffff?
  [c-v]u2192     →
       u251b     ┛
       u2501     ━
       u2517     ┗
       u253b     ┻

Some border characters using [c-v]U and then 8 hex digits
for the unicode.
  [c-v]U0000251b    ┛