To implement an end-to-end blockchain application, we need on-chain codes, Solana network, and off-chain codes. 

On-chain codes are our smart contracts(programs), and you can consider building them as building a backend. After building our programs with on-chain codes, we deploy them to the Solana network via nodes.

Generally, deployed programs to the network need to be run on the client side, such as an interface or a website. Off-chain codes allow the user to interact with on-chain programs more easily by using command lines, interfaces, and 3rd Party SDKs. In this way, transactions and queries can be used and managed by people who do not know how to write smart contracts.

Transactions

Clients run programs on Solana network via transactions. A transaction object contains two parts Signature and Message. 

Signature

Each digital signature is in the ed25519 binary format and consumes 64 bytes Signatures are list of ed25519 curve signatures of the message hash, where the “message” is made up of metadata and “instructions”.

Message

Information that we send to the software as a payload. Consists of 4 parts: Header, Account address, Recent blockhash and Instructions. 

Instructions are the core of the messages, they contain what to do and consists of 3 parts: Program Id, Accounts, Data

We will explain the account structure details in the next video since it is an essential part of the development of Solana programs. To understand program development on Solana better, it is necessary to comprehend 4 core concepts well: accounts, programs, transactions, and PDA’s.

Resources:

https://medium.com/@asmiller1989/solana-transactions-in-depth-1f7f7fe06ac2