Every human being has blood of a certain blood group. So do you.
The main blood groups are:
A (42%), B (8%), AB (3%), and O (47%).

What blood group you are depends on the presence or absence of the factor A and/or factor B on red blood cells.

If you only have factor A, you are blood group A.
If you only have factor B, you are blood group B.
If you have both A and B, you are blood group AB.
If both factors are absent, you are blood group O.

Another factor that determines your blood group is the Rhesus (D) factor, which is a protein-like substance that 85% of people have on their red blood cells.

The presence of this Rhesus factor is specified by a +, while its absence is marked by a -.

The combination of all these factors produces eight different blood groups:
A+, A-, B+, B-, 0+, 0-, AB+, and AB-.

What blood group you get is determined by your parents’ blood groups.

If you have a certain disease or have lost a lot of blood, you may be given blood that comes from another person in a process that is called blood transfusion. Before you can have a blood transfusion, it is important to know your blood group and the blood group of the donor (which is the person whose blood you will receive).

This is because not all blood groups are compatible. If you do not have factor A, B, or Rhesus (D) factor blood, and either of these factors is inserted into your bloodstream through donor blood, your body may ‘reject’ the donor blood. The body will do that by launching an immune reaction.

Someone who is blood group A will make antibodies against the B factor.

Someone who is blood group B will make antibodies against the A factor.

Someone who is blood group AB will not make antibodies against the A or the B factor.

Someone who is blood group O will make antibodies against both the A and the B factor.

If you do not have the Rhesus (D) factor, you may make antibodies against the Rhesus (D) factor.
As a result, you cannot donate blood to just anyone.

Are you blood group AB+? If so, you can receive donor blood from all eight blood groups.

If you are O-, you can only receive O- donor blood.

Still, if you have O- blood, you can give blood to anyone!

And if your blood group is AB+, you can only give blood to someone who also has blood group AB+.

You can always give blood to someone who is the same blood group.

If you do not have A, B, or Rhesus (D) factor, your blood is not compatible with blood that does have either of these factors.

In summary:
Donor blood can be used for a blood transfusion as long as it does not contain any factors that the recipient does not have in their blood.