The two "sides" of the spreadsheet are independent. Normally I just fill out each side in chronological order starting from the top, so you might end up with 10 posts on one side and 6 on the other! So 6 lines will have data on both left and right, and 4 will have data only on one side. Occasionally, I post things ahead of time, for example when the bank tells me it will be taking the service charge (l.o.l) at the end of the quarter, I will leave a gap of say 5 lines below my last post so I have room to post other entries that will fall before the date of the Bank Charge.
You can also "sort" the postings using the normal data sort function in Excel, but take care to only highlight either the left or right sections at any one time when you do this! Using this you can for example make sure everything is in the correct date sequence to check against a bank statement, or group together all entries from the same source.