A factory reset is always a pain, and certainly a terrifying prospect the first time you do it. I'm fairly techy and felt that way too!
As long s your contacts are sync'd with Google, you won't lost them. Log in on a PC and check that you can see them. You could also go into Contacts on the phone and, from the menu, choose Import/Export (it may come under Manage Contacts). If it offers to encrypt, say no. The process will produce a vCard file in the root folder of the device or sd card. Copy this to a PC or cloud storage (eg Google Drive). If everything goes pear-shaped, this is your backup. In fact, I normally recommend this as something to do periodically, just as insurance.
SMS can be backed up by an app called SMSbackup+, which will store them on your Google account.
The easiest way to back up photos etc is to connect the phone by cable to a PC. When it asks how you want it to handle the device, choose the "browse files" option. You can then use the PC file manager to access the phone as a external drive and simply copy the relevant folders.
You can also sync photos to Dropbox or Google Drive - in fact, you should anyway so that you have a backup in case you lose your phone or it simply breaks down. Dropbox will store at full resolution, Google has two options - hi-res, which doesn't count against your allowance, but is slightly compressed, or full-res, which does count.
To restore photos, take one and find it by the PC connection method, then copy the old one back to the same location.
If you choose "restore" when you log back into Google, your apps will restore and your phone should also have all your wifi passwords. You may have to set any app options you've changed manually, though.
The reset process itself is pretty simple, though I would plug the phone in while you're doing it as there's no way of monitoring battery state. In the main settings menu, go into Backup & Restore and look for the Reset option, which may be under Personal Data. What takes care and time is the preparation. There are online guides, but they tend to tell you about booting to recovery mode as well, which you don't need (certainly at this stage) and may make the job seem more complicated than it is. In the past, people have spoke highly of Carphone Warehouse's Geek Squad. I don't know whether they'd do this for nothing if you're not a customer, but they might advise. Make it clear what you want backed up, though.
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