The sleeves go over the top of the Valve Stem and as stated protect the inside lips of the Seals during installation.
What may be confusing is that they do not give you 1 for each seal. The idea is to re-use the sleeve until it looks like it will not work and replace it with another sleeve. They just give you a few extra sleeves.

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84 300D, 82 Volvo 244Gl Diesel