Rims:

Firstly you require the PCD.

PCD – Pitch Circle Diamater and goes through the centre of the stud (see main image)
The adjacent measurement can also be used (S on the image) but is less common.

Measurements are made in either inches if they are exact, or in MM

For example:

Next required is the rim size 14", 15", 16" etc and is measured where the rubber on the tyre fits the shoulder of the rim.
The width is measured between the shoulders as shown in image 3.

So a 5.5×14 5/112 rim reads as:
5.5" wide, 14" rim size, 5 stud with a PCD of 112mm

If a letter is included it relates to the tyre bead profile to define what wheel collar profile you require.

Tyres:

Image 5 shows the number printed on the tyres and what they mea:

tyre width / aspect ratio % /(construction / width / load capacity / speed

so a 195/55R 16 87V tyre reads as: 195mm tyre width with a 55% aspect ratio tyre wall height with radial construction a load capacity og 545kg and a maximum speed of up to 118mph at full load.