Here in England, traditionally, we eat breakfast in the morning. It can be cereal, toast and tea (ie a cuppa). The ‘traditional English breakfast’ is rarely eaten at homes as it’s complicated and an effort. You are more likely to eat it out.
At the end of the morning/beginning of the afternoon we have dinner. It’s a cooked meal. At weekends it’s a Sunday dinner with roast meat and vegetables. You would never call this a lunch.
In the late afternoon/early evening it’s tea. This ‘tea’ is not to be confused with ‘tea’ as in cuppa, the drink, though you may have tea with your tea. You would find people leaving work and going home ‘to have my tea’.
If you are eating out, it’s ‘dinner’. You would never go to a posh restaurant for your ‘tea’. You could go to a tea room for ‘afternoon tea’ and that would be cakes, sandwiches and a cuppa. It is something of a tourist/day out thing.
In the late evening, before bed time, it’s supper. This could be anything. If it’s early, it could be a fish supper ie fish and chips.