You want an off-line contribution (cash or check donation) to count towards the overall fundraising goal reflected in your donation page's progress bar.
You can set goals for your online donation page, which will put a progress bar on the page. If you want an offline donation to count towards a fundraising goal set for a particular page, go to Finances > Donations > New donation, and in the field that reads "Page this donation was from" enter the slug for the page. Now that donation will count towards that page's fundraising goal and increase the progress bar accordingly.
For more information on how to use the donation progress bar effectively, see this clip from NationBuilder Live.