The biggest difference is that an SPA is the sale of all shares, and an APA is the sale of selected assets. Therefore, they are both different transactions and have different procedures.
Once the contract is signed, it's time to start working through the contingencies. For example, the buyer can order an inspection. Additionally, now is the time for the buyer to secure funding for the deal. If all the contingencies are met by closing day, the buyer and seller can complete the transaction.
A SPA is a legally binding contract that sets out the terms and conditions of a sale between a buyer and a seller. It is typically used in the context of buying and selling a business or a significant asset, such as shares in a company.