There's typically no need to worry about the conversion process as a programmer, but it can be useful if you're trying to understand computer architecture.
A logical address is a memory address that the processor can use to access memory. A physical address is the actual address required by the RAM unit to access the data.
Since we're talking about computer architecture, the way to convert between the two varies for different hardware. Generally you have an hardware unit called an MMU (memory management unit) that handles the conversion between logical and physical addresses. It is a fairly complex process because it takes into account memory protection, caching, paging, etc.