These two forms perform completely different activities from the receiving functionality point of view.
Receiving Transactions' form is used to perform the 'Deliver' step to complete the receipts in inventory if the Receipt Routing Method used is 'Standard' (Or 'Inspection' and 'Deliver' steps incase the Receipt Routing Method is 'Inspection Required'). Because incase of 'Direct' Receipt Routing, the receipts are completed in single step, which is performed through 'Receipts' form; But for the receipts routings with 'Standard' and 'Inspection Required', we need to complete the receipts in 2 & 3 steps respectively using 'Receiving Transactions' form as mentioned above.
Whereas 'View Receiving Transactions' (Or 'Receiving Transactions Summary') form is used to view the receiving transactions performed for the particular PO, item, or the date range as per the input parameters passed. This form doesn't perform any receiving transactions.
I hope this answers your question.