WHAT IS A GENOTYPE?
A genotype is the entire genetic constitution of an individual, i.e. genetic makeup of an organism or group of organisms with reference to a single trait, set of traits, or an entire complex of traits. In a nutshell: your genotype is your complete heritable genetic identity; the sum total of genes transmitted from parent to offspring.

There are 4 hemoglobin genotypes (hemoglobin pairs/formations) in humans: AA, AS, SS and AC (uncommon). SS and AC are the abnormal genotypes or the "sickle cells". We all have a specific pair of these hemoglobin in our blood which we inherited from both parents.

WHY IT'S IMPORTANT TO KNOW YOUR GENOTYPE
Knowing one's hemoglobin genotype before choosing a life partner is important because there may be compatibility issues which could have devastating effects when it comes to conception.

Individuals with sickle cells experience severe pains in body parts where oxygen flow is compromised due to blockage in the blood vessels.

-- AA can marry anybody
-- AS is better off with AA
-- AS and AS, AS and AC are too risky
-- Two sickle cells = avoid conception!

WHAT IS A BLOOD GROUP AND TYPE?
To classify blood, antibodies and inherited antigenic substances on the surface are evaluated.
There are 4 blood GROUPS:
-- Type A (marker A)
-- Type B (marker B)
-- Type AB (blood cells have both A and B markers)
-- Type O (blood cells have neither A or B markers)

AN ADDITIONAL MARKER IN BLOOD: RHESUS FACTOR
This is simply a protein that may be present on the surface of red blood cells. Some people have it and others don’t. If you have it, your blood type is further classified as positive; if you don’t, your blood type is further classified as negative. It is just a genetic difference (e.g. blue VS green eyes) and nothing to worry about. Therefore present Rhesus factor = Positive. No Rhesus factor = Negative.

BLOOD TYPES
O- = No A or B Marker
O+ = No A or B Marker + Rhesus factor (One of the Two Most Common Types)
A- = A Marker Only
A+ = A Marker but No B Marker + Rhesus factor (One of the Two Most Common Types)
B- = B Marker Only
B+ = B Marker but No A maker + Rhesus factor
AB- = A and B Markers Only
AB+ = All 3 Types of Markers: A, B and Rhesus factor

WHY IT IS IMPORTANT TO KNOW YOUR BLOOD GROUP COMPATIBILITY
It is important to know your blood type if you need a blood transfusion or want to donate blood. It also plays a role in determining paternity. Before a blood transfusion takes place it must be established that the donor’s blood type is compatible with the recipient’s. Combination of certain antibodies (proteins protecting the body) can be harmful or even lead to fatal symptoms if antibodies perceive foreign cells as a threat. It is our immune systems’ way of protecting us.

TYPES OF BLOOD TEST
-- Complete Blood Count (CBC)
-- Blood Chemistry Tests
-- Blood Enzyme Tests
-- Blood Tests to Assess Heart Disease Risk.

SOURCE (abridged): https://www.thebridgeclinic.com/blog/why-is-it-important-to-know-your-genotype-and-blood-group-compatibility