Hi, and welcome! As
@CottonTexas said above, use the forums (and their search function)! If there is one rule in the SFF world it is that there is no such thing as one size fits all, so a beginners guide would be a rather impossible thing to make. Still, there are some things that are useful to keep in mind, at least the way I approach this.
First off, the obvious stuff: know what you will be using the PC for, where (one place or moving?), and what you are willing to spend in terms of both money and time.
Given that you are here on the SFF forums and form factor thus ought to be important to you I would then start out by looking for a case. If you have hardware in mind already, keep that in mind when looking - can it fit, and can I cool and power it in the case I'm looking at? If not, the case will often be limited in terms of what will fit, so keep your use case in mind. If you want a powerful gaming rig but your case only fits low profile add-in cards, that's not going to work. And so on.
Once you get into cases you'll start learning about power delivery, as that's often the most defining factor of each case. In essence there are four broad categories of SFF power delivery case compatibility, which we can sum up like this:
- Easy: fits standard ATX or SFX(-L) PSUs - cases from mass-produced ITX cases to the SFF standards like the Dan A4 or Ncase M1, with an ever-growing selection of options.
- Rare: still standard, but odd/unusual standards with less PSU choice like TFX, FlexATX or 1U server PSUs. Plenty of cases like this in both the case design subforum and the "What's on Taobao" thread.
- Bricked: uses an external power brick with an internal DC-ATX board from HDPLEX, mini-box or other source. Cases can get very, very small, like the NFC Skyreach S4 Mini.
- And finally Brickless - uses DC-ATX boards like those with bricks, but with an internal instead of external DC source. Some cases are made like this, but often brickless builds consist of modding a case to fit an internal AC-DC PSU despite it not being meant for this. There are some very impressive S4 mini brickless builds on these forums, but these are not undertakings for the faint of heart/wallet/free time. Some cases are also built for internal brickless power, often using either internal HDPlex units or MeanWell AC-DC converters.
Each of these categories has pros and cons, either in complexity, size, max power output, noise, availability, thermals, price, or any combination of the above. Small, cheap and powerful is usually also hot, loud and unreliable. Easy, affordable and powerful is usually large. Etc., etc. Make your choice depending on what you prefer - but beware that the rabbit hole of no-compromises SFF can be very, very deep. A lot of the reason for the popularity of the M1, A4 and similar cases is their relative ready-to-use nature and relatively broad hardware compatibility despite a relatively small size.
Once you have found the case you want, the time has come to plan your build. What this entails depends on your case/build class. Builds in the Easy class still require planning and checking compatibility, and can require careful planning or even modding if you want something slightly ambitious like fitting a tiny AIO into a case not really made for it. Make sure your CPU cooler fits your case, that your GPU not only fits but that its power plugs fit and that you'll be able to actually install the card, etc. On the other end of the spectrum you have builds requiring you to solder your own power cabling, or even build custom PCBs for power distribution. Luckily for most of us few builds need to land at the extreme end of this, but for those with proclivities like this, the options are there. Bricked builds are often an excellent compromise, giving massive performance in tiny packages as long as you can live with an external power brick. I can't, so they're not for me, but going with a power brick can allow for a relatively "easy" tiny and powerful build like stuffing an RTX 2070 and R7 3700X into an S4 Mini with minimal tinkering.
When you (inevitably) get stuck: ask us for help! There are people here with massive amounts of experience, and most of them are very, very helpful and friendly. The amount I've learnt in the couple of years I've been here is immense, so don't be afraid to ask. The SFF.Network Discord is also a very useful place for more off-the-cuff questions that don't necessarily warrant a thread or new post in a build thread.
Happy hunting/planning/building, and again, welcome!
