I get asked about this a fair bit so here is my HD security cam 101.
First things first
Do not bother with analog cams or anything less than 720p. The video is almost useless and they will cost as much or more than HD cams.
The 2 trickiest bits are getting power to it and getting it connected to your network.
You can find these 720p Escam QD300s for as little as $27 on Amazon if you wait long enough. Generally they are $35-$40. I prefer these Escam QD900s today. Above pic is from one. They are 1080p which really makes a difference. I’ve seen them as low as $43 used. Been trending around $55. If mounting on or near the house, run an Ethernet cable to them and you can power them off the Ethernet cable by using some cheap POE adapters. Note this will not work with 5 volt cameras but fine for these 12 volt models. Away from the house just use WiFi. Do NOT run unshielded Ethernet outside for more than a few feet or a storm may fry your network! You can pick up cables for analog video cameras pretty cheap. For some reason they are cheaper and longer than the power only cables. My creek cam is on about 200 feet cable run, which is about the limit and probably is hurting the image quality a bit at night. Unless you have enterprise class WiFi or a repeater, you are not going to go much farther anyway through trees anyway. Waterproof any connections / unused connectors with duct tape or sticking in a waterproof outlet box. Be sure and change ALL the default passwords, user and P2P! I generally like to set up cams so each cam is visible to another so if someone, or more often something, messes with it I know what happened to avoid it happening again. Note the affordable 2k cameras are just starting to come out so you might want to keep that in mind when planning purchases. Check out Amcrest IP3M-941W and Amcrest IP3M-943W (Note I have not tried one of these yet but have eval coming.) Also if you feel comfortable taking electronics a part you can swap the lenses out on those QD cameras to get up to a 4x zoom from a 16 mm lens. That will help keep you camera closer to the house and less noticed.
There are all kinds of recording options.
The cameras above come with info on their cloud based service and there are lots of others but I generally find them pricey and you can easily swap your internet connection. There are also some nice looking DVR boxes now but I prefer a PC running Blue Iris. If you are just doing a cam or two, about any old (unfortunately has to be Windows) PC will run it just fine. For instance a used PC if you do not have an old one laying around. A single i7 class PC (as low as $600 new) can handle about 18 720p cameras recording continuously. (You can have them only record when they see motion but I would not suggest it.) After running a few days see how much space your recordings take with your settings and get a second hard drive for it. Given you might not notice or hear about something you want to review the video for right away I general suggest keeping at least a week’s worth. 8 TB drives are available now at a decent price per gigabyte. Just saying. I generally go with Western Digital Red or Purple. Blue is a bit cheaper but had some of those fail on me in less than a year. Your mileage may vary. For more on WD colors click here.
From there it depends on how wild you want to get.
Blue Iris is pretty easy to get running and has a ton of stuff you can get fancy with if you want to take the time. Definitely start by setting it up so you can view on your phone. Then setting motion alerts based on something above at least certain size moving between (up to 8 odd shaped) areas of the picture. Motion detection is something you will just have to play with till you get the sensitivity and screen zones right. Once you do, you can have it alert you to odd behavior in a bunch of ways. For instance one of mine says "driveway" over speakers and uploads a pic to my cloud if it sees something moving on the driveway, with a rectangle drawn around the thing it saw. I have that camera aimed at the gate at the street and I've told it to ignore anything beyond the gate and be extra sensitive to any motion near the UPS box out there. (UPS seems scared to drive in my driveway and used to just leave stuff sitting by the gate or random spots in the yard so now there is a box for them near the gate.) It is SO nice while I'm working to only have to glance at a monitor to see what is in the driveway or what the dogs are barking at. Especially lately if I had to go outside to check on them every time they get stirred up I'd never get anything done. Add to that seeing the wildlife you might not even know had in your yard and you will probably be adding more cams than you ever thought you would want for security. FYI for those that do not know, check out 3 camels price watch You can set it to email you when an item on Amazon falls below a price you are willing to pay! Also shows you historical prices for an item so you know what is a good price and right time to buy. Can save you BIG money!