ばんごはんのあと、べんきょうするつもりです。

つもり  is used to state an "intention." So the above sentence means “I’m planning to study after dinner.” You usually use non-past plain form before つもりです and if you intend “not to” do something, you can also use it with a negative form.

パーティーにはいかないつもりです。(I intend not to go to the party.)

This is almost the same as: パーティーにいくつもりはありません。(I don’t have any intention to go to the party.) but the latter has a stronger denial.

You can describe your past intention, which did not eventuate, using つもり as well.

ばんごはんのあと、べんきょうするつもりでしたが、テレビをみてしまいました。(I intended to study after dinner but I ended up watching TV.)

However, if you use past tense before つもり the meaning can change from  "intention" to “conviction” or “assumption.”

わかったつもりだったけれど、じっさいにはわかっていなかった。(I thought I had understood but actually I did not.)

アイスクリームをかったつもりでちょきんします。(I’ll put away the money I would have spent on an icecream.)