Once you believe your cow to be bred, I highly recommend testing to be sure. Drawing blood is probably the simplest way to test and can be done 30 days post-breeding on an open cow. If your cow has a calf on her, you also have to wait 90 days post-calving for the blood work to be accurate. I have personally had horrible experiences with vets palpating, although that is another option. I'm not sure if mini's feel different or what, but multiple times have been wrong. (I do love and trust my vet.) You can do blood testing yourself, check out Biopryn for an easy option.
OK... THE DAY is here. What's in your emergency calving kit??? I can tell you what I have in mine, and it changed as each minor emergency has happened. I have a "go bag." In it is pulling chains (which I have been fortunate not to use yet), handles, lube, palpation sleeves, towels, iodine, a GOOD flashlight, extra batteries, and Karo syrup. I have powdered colostrum in my freezer, a bottle, and hay and feed ready for a peace offering. Everything loaded into a 5-gallon bucket. Most of the time, everything goes just as it should. The tail sticks straight out, water bag appears, followed by two feet and a nose. In a heifer, I expect to see progress every hour and call for help if that's not happening. In a cow, I expect to see everything move along within an hour. If you see anything abnormal, call someone. I believe it is a courtesy to inform your vet (or neighbor) that you have a cow about to calve and may need help. Have a plan of what to do, when to do it, and whom to call (along with phone numbers) If you think you need help, ask for it, time can be critical.
A heifer begins cycling between nine months and 22 months, but should not be bred until at least 65% of her mature body weight. This is generally around 15 months of age. Cows cycle into heat approximately every 21 days (give or take a few.) Signs of heat include vocalizing, riding other cows, discharge, being trailed by your bull, and standing to be mounted. You track heat cycles to have a good idea when your cow was bred. Then, enter the date into a cattle gestation table and you have the due date. (The link goes to one I like from "Cattle Today.") There are a few apps that help track and keep records. You could also just keep a calendar or notepad. Just remember, good record keeping is essential!!
Now, your cow is bred, she is due any day. How do you know when the day is THE DAY?? They all look a little different. The first thing I notice is that the cow is definitely bagged up. Her teats start pointing out and there is a small amount of waxy discharge on the tips. If she lets you squeeze them, milk comes out easily. When viewed from behind, the cow starts to "spring." (Ask me for pictures, they can be kinda gross. If you need to know, I'm happy to share them. I did take the pictures after all.) Then one day, she looks skinny. You know you've been feeding this girl, so it makes no sense. Except... the baby is getting into position. Her belly drops from out to down as the calf starts pointing its nose toward the exit. The ligaments in the pelvis loosen and her hip bones appear more prominent. She's physically getting ready for that baby. Finally, just before she's due, the day or hours, she starts carrying her tail. The tail is up away from her body. She may be restless or not, eating or not, and trying to find a quiet place or not. If it's a first calf heifer, good luck with that and all the steps preparing for delivery. They don't always follow the rules.
Now... Calf in on the ground, what do you do? Make sure the sack is not covering the nose. Break it if it is, tickle the nose with hay or long grass to help clear the airway. Don't get killed by mom. The friendliest cow in the world may have a different opinion of you when she has a calf on the ground.
If everything is going well, Do Nothing! Let the calf and cow bond. You should see her licking and cleaning, in bad weather you can help dry if she'll let you. Try not to get fluid on you, it makes mom inspect you a little too close.
In the first four hours, you want to see that calf stand and nurse. The calf has 24 hours to absorb colostrum, if you miss that window you will have a sick calf unless you go above and beyond. (you can have antibodies delivered in a blood transfusion.) This is where having colostrum on hand can come in handy. Calves born in the heat of the summer definitely have a harder time getting active. Spraying the umbilical cord with iodine can help prevent a number of issues.
Then, you want to see the calf poop. The last thing I'm looking for is all 4 quarters nursed. This for the cow's health, not the calf's. It is fine if it takes a week, but not too much longer. The best advice, if you have a bad feeling, call someone, you're probably right. If you were overreacting, that's better than under-reacting. As with calving, there is a limited time when things need to happen, to prevent major problems.