GoReda

        payer = buyer,        space = Order::SPACE,        seeds = [b"order", buyer.key().as_ref(), product_id.to_le_bytes().as_ref()],        bump    )]    pub order: Account<'info, Order>,     #[account(        init,        payer = buyer,        space = EscrowAccount::SPACE,        seeds = [b"escrow", order.key().as_ref()],        bump    )]    pub escrow: Account<'info, EscrowAccount>,     pub system_program: Program<'info, System>,} #[derive(Accounts)]pub struct ConfirmOrder<'info> {    pub seller: Signer<'info>,     #[account(mut, has_one = seller)]

1. Line 195 seeds = [b"order", buyer.key().as_ref(), product_id.to_le_bytes().as_ref()],: Declares the PDA seeds. Anchor re-derives the address and rejects the account if it doesn't match.
2. Line 196 bump: Uses the bump seed, the extra byte that pushes the derived address off the ed25519 curve.
3. Line 201 init,: Creates and pays for a new account. Space and payer must be specified.
4. Line 214 pub seller: Signer<'info>,: Requires this account to have signed the transaction.
5. Line 216 #[account(mut, has_one = seller)]: Checks that a stored pubkey field matches the passed account.

use anchor_lang::prelude::*;use anchor_lang::system_program; use crate::state::EscrowAccount; /// Transfer SOL from buyer (signer) to escrow PDA via system_program CPI./// This works because the buyer is a signer and system-owned.pub fn fund_escrow<'info>(    from: &Signer<'info>,    to_escrow: &Account<'info, EscrowAccount>,    system_program: &Program<'info, system_program::System>,    amount: u64,) -> Result<()> {    let cpi_ctx = CpiContext::new(        system_program.to_account_info(),        system_program::Transfer {            from: from.to_account_info(),            to: to_escrow.to_account_info(),        },    );    system_program::transfer(cpi_ctx, amount)?;    Ok(())}

1. Line 9 from: &Signer<'info>,: Requires this account to have signed the transaction.
2. Line 14 let cpi_ctx = CpiContext::new(: Makes a cross-program invocation into another program.