A lot of you cannot differentiate between veins and arteries and when I hear you people mixing them up, I feel like I owe it to you people to correct you when in actuality, I don't owe you people but what type of neighbor would I be if I cannot help with simple corrections like this. Do not bother thanking me now, wait till the end of the post so you can make the appreciation double.
So, like a child who is still suckling. Generally, arteries take oxygenated blood away from the heart, and veins take deoxygenated blood to the heart. I hope I am correct, not mixing things up because these things can be easily mixed up. It is easier to explain the arteries get force from the pumping of the heart as well as gravity allowing them to send blood to the soft tissues but it is very difficult to explain how the blood goes back to the heart from regions that are far from it especially when there are no such force to return them which usually happen when we are in dependent positions. For these to happen, the body depends on some mechanisms including walking, or performing activities with our legs in what is referred to as calf muscle pumps.
Another way we can get blood back to the heart is when we breathe and this happens through a kind of bellows effect as a result of our chest getting expanded giving a negative pressure in the chest that creates a vacuum allowing blood to be sucked back into the heart. Another reason why blood flows easily from arteries is the absence of valves which are present in veins. The valves help to close blood that has gone upwards, preventing it from going down.
In cases like Varicose veins, the veins suffer from venous insufficiency where the valves are not functioning properly. This can happen through inflammation or any other reason causing the valve to become slack and the blood to not move well. Once the valves become dysfunctional or destroyed, gravity begins to pull the blood downwards to the leg and away from the heart.
What I just explained might sound simple but there are a lot of things that could go wrong including leg swelling, and skin changes. When a person suffers from varicose veins, they have venous insufficiency but it is possible to have venous insufficiency and not suffer from varicose veins.
You wonder what varicose veins look like, they are those veins that show up underneath the skin like lightening strike, the ones you refer to as spider veins. They could be cosmetic sometimes but the majority of the time, they are caused by Varicose veins.
People who suffer from this can experience pain, itching, swelling, burning or throbbing sensation, burning, heaviness and uncomfortable legs. A lot of people do not see this as a big deal and so they do not go to the hospital or see a doctor but let me say this to you that while you might think it's nothing serious, it could be as a result of other underlyin factors including blockage to the veins.
You Can Further Study Here
https://www.healthdirect.gov.au/varicose-veins
https://www.hopkinsmedicine.org/health/conditions-and-diseases/varicose-veins
https://www.nhlbi.nih.gov/health/varicose-veins
https://www.alliedtherapy.au/chronic/copy-of-chronic/copy-of-lipoedema
https://www.medi.de/en/diagnosis-treatment/venous-disorders/varicose-veins/
https://www2.hse.ie/conditions/varicose-veins/