The direct equity investment in a company is provided by its "ordinary " shares.

Made popular by privatisation the share is ideal for the punt on an interesting company, but if it goes bust you lose your money.

Shares carry voting rights so they are good buy for AGM activists.( This is when ethical / environmental / consumer activists buy shares in order to have a right to attend meetings and ask awkward questions).

May provide special deals and discounts on company goods and services.

If you think you know something that the market doesn't buying could make you a lot of money, ( as long as you are not insider dealing ). ( E.g. in Canada a geology student in found some ore out in the wilds. The professor had heard that exploration permits had been sold. They found out which penny share company had the permit for the area, bought as many shares as they could, then gave the company the good news. Or so goes the story).

They can be used in ISAs and PEPs.

Tax

Dividend income subject to Income tax, share sales to Capital Gains Tax.

CGT calculations can be complex. Always keep all bits of paper or you may face a tax bill that, if all the information was to hand, might be reduced.