Within Google Sheets, you can add tasks to your projects using the Teamwork add-on.
The add-on can be installed directly from the G Suite Marketplace. Once you click install, you can select and authorize which Google account you want to use to install the add-on.
You will then see Teamwork Projects for Google Sheets listed as an option in the Add-ons dropdown when you have a document open in Google Sheets.

You can also set up the add-on from within a sheet. When you have a document open, click Add-ons in the horizontal menu bar and select Get add-ons from the dropdown.

In the add-ons modal, use the search field in the top right to search for Teamwork Projects. Click the add-on card to open the details view.

You will be asked to select which Google account you want to use with the add-on.
Once you Allow in the permission access window, you will then see a new Teamwork Projects for Google Sheets option in the Add-Ons dropdown.

Click the Add a task option to open the Teamwork add-on on the right-hand side of your sheet. Here, you can either log into an existing Teamwork account or sign up to create a new one.

Once you have entered your Teamwork credentials, you will also need to grant access permissions to your account for the add on.
To add a new task to your Teamwrok site, select the Add a task option from the dropdown.
In the quickly add tasks modal, you can select a project to add the task(s) to. To add multiple tasks to the project, put each task on a new line.

Task properties
You can use various commands to assign properties to the tasks, just like when posting tasks via email:
- (bugs) or [#bugs] - specify an existing task list to add the task to (task list name needs to match exactly).
- @name - assign the task
- [tomorrow] or [15/09/2019] - set the due date
- [start date][due date] e.g. [today][next monday] - set start and due dates
- ! - low priority
- !! - medium priority
- !!! - high priority
- #tag - add a tag to the task
Note: When setting a start date and due date, the system will automatically use the later date entered as the due date.
Options
- Attach this Sheet link to task - the link for the sheet will be added to the description of the task
- Add comment to Google Sheet - create a comment for the task in the Google Sheet
Logging out
To log out of your Teamwork account, select your profile icon in the top right corner of the add task modal and select Log Out.

For more information, see: Using the Google Docs Add-on