Very sorry to hear about the refusal.
Do you have the letter they sent explaining the reasons? If so, and if you are comfortable with it, you can post the exact wording (with personal details redacted) and we can offer feedback if we can. The letters are usually worded very carefully; if we see the exact text that would be helpful.
Unfortunately, if you have a refused visa, it is highly recommended you get a visitor visa in advance before trying to enter the UK. It's not a set-in-stone rule, but it is unlikely that someone with a previously refused visa application can enter the UK without prior entry clearance... and it being so soon and for a settlement visa, IMO, it's risky.
If the reason for the refusal is missing documentation, and it's something you can address, it will be easiest and quickest to re-apply for the visa and supply the missing documents. An appeal is generally only successful if all the required paperwork was provided with the original application, and the ECO overlooked it. Additionally, an appeal generally takes about a year. So if you just need to include further evidence of finances, it will most certainly be faster to submit a fresh application.