Buying shares - Cheapest/Best way to purchase?

[Froomee]

As the title says.

Iv looked online and information is fairly basic so thought I'd ask here.

Who do you buy shares with? Who is the cheapest, are there any obvious pitfalls to avoid.

The amount id like to potentially invest is £10-£20k and possibly adding to it monthly.

Thanks in advance to any help.

[Froomee]

A bit of both to be honest.

Iv been looking at buying another house (which I may well do) but I'm reluctant to put all my money into houses.

I might buy a cheaper house and put the rest into shares rather than having all my eggs in one basket so to speak.