You and - say a housing association own the property jointly - the % you own can vary 40,50 or 75% for example.

 If you own 50% then you get a mortgage for 50% of the property value and pay the Housing Association rent on the other 50%.

Advantages - gets you on the housing ladder, you share in any increase in the property value, you can buy a higher % of the property at a later date - but at the market value at the time. 

Disadvantages - not all mortgage lenders accept these schemes, you have to pay rent on the bit you don't own, any improvements you make to the property you pay for in full - but the housing association get half of the capital appreciation when you sell, you are restricted to what you can raise capital for on the property, any alterations have to be approved by the housing association,the mortgage process is more complicated.

If you can afford a house yourself  buy one outright - if you can't go shared ownership - assuming you are accepted by the housing association - there is normally a lot of people after these properties and it can take a long time to find out if you are accepted.