Clicar vs. carregar
The difference between clicar and carregar regarding computer interactions is primarily regional. While clicar is a direct adaptation of the English word "click" and is used universally, carregar is specifically used in European Portuguese (Portugal) to mean "to press" or "to click". In Brazil, carregar usually means "to load" or "to charge" and is not used for mouse clicking.
Clicar
A2This verb is derived directly from the English "to click". It is the standard term used in Brazilian Portuguese for pressing a mouse button or tapping a screen. It is also used in Portugal, though it often competes with carregar.
Você precisa clicar no link para abrir o site.
(You need to click on the link to open the site.)
Se você clicar duas vezes, a pasta vai abrir.
(If you click twice, the folder will open.)
Eu tentei clicar no botão de cancelar, mas travou.
(I tried to click the cancel button, but it froze.)
Ao clicar na imagem, ela aparece em tela cheia.
(By clicking on the image, it appears in full screen.)
O mouse está quebrado e não consigo clicar em nada.
(The mouse is broken and I cannot click on anything.)
Carregar
B1In European Portuguese (Portugal), this word describes the physical act of pressing or pushing a button, key, or mouse. In Brazilian Portuguese, this word almost exclusively means "to load" (data) or "to charge" (a battery), so using it to mean "click" can cause confusion there.
Carregue no botão direito do rato para ver as opções.
(Press the right mouse button to see the options.)
Quando o aviso aparecer, carregue em OK.
(When the warning appears, click OK.)
Por favor, não carregue em nenhuma tecla agora.
(Please do not press any key right now.)
Tens de carregar aqui para submeter o formulário.
(You have to click here to submit the form.)
Se carregares no link, serás redirecionado.
(If you click on the link, you will be redirected.)
Summary
In short, clicar is the universal term for "clicking" a mouse, dominant in Brazil and common in Portugal. Carregar means "to press" or "to click" specifically in Portugal. However, be careful using carregar in Brazil, as it is understood as "to load" (a webpage/program) or "to charge" (a device).