how can i create a fillable table

You can use the Matrix field:

This field allows you to select different input types. Select rows (top menu) to add the row categories. Select columns to add column categories.

You can test it here:

http://form.jotformpro.com/form/50754333783964? 

Let us know if we can assist you further.

Thank you!

This is a follow-up question. I want to create a table as a student exercise. I will have some cells with the data entered and others that are 'empty' which the students will fill. The data the students will enter is is all numeric. Can I use a similar approach to the above? Also if I want several groups working on the same exercise but mot the same form, do I have to create several forms with the same data? Thanks. 

If you need an actual spreadsheet in the form, you can add a spreadsheet widget:

http://widgets.jotform.com/widget/spreadsheet

Several people can fill out the same for at once.  Each time the form is submitted, the form will be forwarded to your JotForm account.  Unless you need the form itself to be different for each person, there is no need to create more than one form.

Thanks, David. What I want is say 5 goups of students working on a unique solution to the originsl problem (created by me). Within each group, the students will collaborate, but each group will need their own problem table/spreadsheet that cannot be accessed by others. I think you're saying is thst  it's posiible to collaborate on one form which works inside a group. I'm wondering if each group will need its own copy of the original form. -S

PS -- I read the spreadsheet widget reviews & apparently the column (and row) headings cannot be chsnged. Has that issue been adressed? That's why I thought a table (as described above) might be a better idea. -S

Our forms collect data from single entries.  The user fills out the form, presses the submit button and the data is forwarded to your JotForm account.  If you need a spreadsheet that can be updated by multiple people over time, something like Google Docs would be much more suited.  Since this is a rather old thread, if you have further questions regarding your specific requirements, please create a new post details those specifics and we will be happy to help.