If you are earning over £10k pa you should have been enrolled into a workplace pension scheme. If this hasn't happened you need to raise this with your employer.
You can have a private one at the same time but your employer will only pay into one. When/if you leave that employer the money you paid In will still be yours. If you think you will have a number of jobs you could have a private pension and transfer your workplace schemes into the private one when you leave so that at retirement you have one big pot.
While you are younger your money will be held in riskier finds so that it increases throughout your life. This means that as the cost of living rises so will your pension fund. To put simply, say a loaf of bread costs £1 now, when you get to retirement it might cost £2. If you invest in a pension your £1 will increase to £2. But if you put into a savings account that £1 might only increase to £1.50 meaning you can buy less when you get older.
As your funds are held in riskier funds when you are younger the idea is that your pension fund will be going up and down. If it goes down (which it did do with COVID) it doesn't matter so much because you have 30+ years for the market to recover. As you get closer to retirement age your pension fund will move to safer funds to protect you from the market going up and down (basically so that if Covid happened as you retired your funds are invested safely so the value doesn't fall right when you are about to retire).
You can ask your pension provider to put your money into safer funds but you won't get the increase in market value over time.
When you retire there's a number of things you can do from cashing the whole fund in or buying an annuity so you get a regular income.
If you are paying in through your work place then the minimum is 5% from you and 3% from your employer. You also get tax relief meaning that you pay, for example, £80, you get £20 tax relief and £60 from your employer. So £160 goes into your pension but it only costs you £80. So that's doubling your money.
There's no right or wrong way to save for your retirement so long as you do (unless u are happy to live on the state pension of £170 per week)
Even if you only paid into your pension for a year you will have £1,920 (160x12) but it's only cost you £960 (80x12).