Please see this sample tax transcript from the IRS.
As you can see, the bold headings identify categories which, because of the several redesigns of the 1040, contains items that are no longer all together on the same form.
For example for 2019, under Income, you see "WAGES, SALARIES, TIPS, ETC:" - this is line 1 on the 1040. But you also see "BUSINESS INCOME OR LOSS (Schedule C):", which is line 3 on Schedule 1(1040).
This means that you have to be a little flexible and try to match the description on the transcript with the description on the actual tax return.
If you are going to be looking at forms for 2018, the 1040 was accompanied by five Schedules (1-5) whereas the 1040 in 2019 had only 3.
2018 1040 - https://www.irs.gov/pub/irs-prior/f1040--2018.pdf
2018 Schedule 1 - https://www.irs.gov/pub/irs-prior/f1040s1--2018.pdf
2018 Schedule 2 - https://www.irs.gov/pub/irs-prior/f1040s2--2018.pdf
2018 Schedule 3 - https://www.irs.gov/pub/irs-prior/f1040s3--2018.pdf
2018 Schedule 4 - https://www.irs.gov/pub/irs-prior/f1040s4--2018.pdf
2018 Schedule 5 - https://www.irs.gov/pub/irs-prior/f1040s5--2018.pdf