<?xml version="1.0" encoding="UTF-8"?>
<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
    <fullName>MyExternalId__c</fullName>
    <externalId>true</externalId>
    <label>MyExternalId</label>
    <length>255</length>
    <required>false</required>
    <trackFeedHistory>false</trackFeedHistory>
    <type>Text</type>
    <unique>false</unique>
</CustomField>

"Name","Phone"
"Salesforce Data Loader","(415)901-7000"
"CRM Science, Inc.","(484)775-0333"

#Account Insert Mapping values
Name=Name
Phone=Phone

"FirstName","LastName","AccountId"
"Astro","Sillet Buxton","0014W00002AKpQZQA1"
"Cloudy","Sillet Buxton","0014W00002AKpQZQA1"
"Appy","Sillet Buxton","0014W00002AKpQZQA1"
"Codey","Sillet Buxton","0014W00002AKpQZQA1"
"Nate","Pepper","0014W00002AKpQaQAL"
"Joe","Griffith","0014W00002AKpQaQAL"

#Contact Insert Mapping values
FirstName=FirstName
LastName=LastName
#Make sure to update Account IDs after account insert!
AccountId=AccountId

ID,FIRSTNAME,LASTNAME,PHONE
0014W00002AKpQZQA1,Astro,Sillet Buxton
0014W00002AKpQZQA1,Cloudy,Sillet Buxton
0014W00002AKpQZQA1,Appy,Sillet Buxton
0014W00002AKpQZQA1,Codey,Sillet Buxton
0014W00002AKpQaQAL,Nate,Pepper
0014W00002AKpQaQAL,Joe,Griffith

#Contact Update Mapping values
Id=Id
#Try not to include anything in the mapping if you're not going to update it
#Preferably omit any columns you're not updating from the source file as well
Phone=Phone

"ID","NAME","PHONE","STATUS"
"0014W00002AKpQZQA1","Salesforce Data Loader","(415)901-7000","Item Created"
"0014W00002AKpQaQAL","CRM Science, Inc.","(484)775-0333","Item Created"

"ID","FIRSTNAME","LASTNAME","ACCOUNTID","STATUS"
"0034W00002IrSv0QAF","Astro","Sillet Buxton","0014W00002AKpQZQA1","Item Created"
"0034W00002IrSv1QAF","Cloudy","Sillet Buxton","0014W00002AKpQZQA1","Item Created"
"0034W00002IrSv2QAF","Appy","Sillet Buxton","0014W00002AKpQZQA1","Item Created"
"0034W00002IrSv3QAF","Codey","Sillet Buxton","0014W00002AKpQZQA1","Item Created"
"0034W00002IrSv4QAF","Nate","Pepper","0014W00002AKpQaQAL","Item Created"
"0034W00002IrSv5QAF","Joe","Griffith","0014W00002AKpQaQAL","Item Created"

"FirstName","LastName","MyExternalId__c"
"Nathaniel","Paprika","867-5309"