Access control has a model to which it grants permissions, the permissions it grants and optionally a group.
Access controls are additive, for a given model a user has access all permissions granted to any of its groups:
if the user belongs to one group which allows writing and another which allows deleting then they can both write and delete.
If no group is specified, the access control will be applied to all users, otherwise will be only applied to the members of the given group.
Available permissions are creation (perm_create), searching and reading (perm_read), updating existing records (perm_write) and deleting existing records (perm_unlink)
For example code is like below...

id,name,model_id:id,group_id:id,perm_read,perm_write,perm_create,perm_unlink
access_pos_order,pos.order,model_pos_order,group_pos_user,1,1,1,1
access_pos_order_line,pos.order.line,model_pos_order_line,group_pos_user,1,1,1,1
access_pos_order_manager,pos.order manager,model_pos_order,group_pos_manager,1,0,0,0
access_pos_order_line_manager,pos.order.line manager,model_pos_order_line,group_pos_manager,1,0,0,0
access_report_transaction_pos,report.transaction.pos,model_report_transaction_pos,group_pos_manager,1,1,1,1
access_account_journal_pos_user,account.journal pos_user,account.model_account_journal,group_pos_user,1,0,0,0
access_account_move_pos_user,account.move pos_user,account.model_account_move,group_pos_user,1,1,1,0
access_account_account_pos_user,account.account pos_user,account.model_account_account,group_pos_user,1,0,0,0
access_stock_picking_pos_user,stock.picking pos_user,stock.model_stock_picking,group_pos_user,1,1,1,1
access_sale_shop_pos_user,sale.shop pos_user,sale.model_sale_shop,group_pos_user,1,0,0,0
access_pos_order_stock_worker,pos.order stock_worker,model_pos_order,stock.group_stock_user,1,0,0,0
access_stock_move_pos_user,stock.move pos_user,stock.model_stock_move,group_pos_user,1,1,1,1
access_report_sales_by_user_pos,report.sales.by.user.pos,model_report_sales_by_user_pos,group_pos_user,1,0,0,0
access_report_sales_by_user_pos_month,report.sales.by.user.pos.month,model_report_sales_by_user_pos_month,group_pos_user,1,0,0,0
access_report_sales_by_margin_pos,report.sales.by.margin.pos,model_report_sales_by_margin_pos,group_pos_user,1,0,0,0
access_report_sales_by_margin_pos_month,report.sales.by.margin.pos.month,model_report_sales_by_margin_pos_month,group_pos_user,1,0,0,0
access_report_pos_order,report.pos.order,model_report_pos_order,group_pos_user,1,1,1,1